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5. Infertility in cows


5.1 Congenital morphological causes
5.2 Functional causes of infertility and repeat breeding
5.3 Infectious causes of infertility
5.4 Summary
5.5 References


Cattle are deemed infertile when they are neither normally fertile nor completely sterile. Interest in bovine infertility increased with the introduction of artificial insemination in the 1950s and as the factors involved became known to farmers, herdsmen physiologists and other workers (Roberts, 1956).

The causes of infertility are many and can be complex (Arthur, 1982). They relate to Graafian follicle development and maturation, oestrus onset, successful coitus, ovulation, fertilization, implantation, and the development and delivery of the foetus and its membranes. Anything interfering with these routines, such as diseases, poor nutrition, inadequate herd management, hereditary and congenital factors, hormonal disturbances or environmental changes, makes the animal infertile, if only temporarily (Osmanu, 1979).

Ten to 30% of lactations may be affected by infertility and reproductive disorders (Erb and Martin, 1980), and 3-6% of the herd is culled annually in developed countries for these reasons. The extent of the problem is likely to be similar in the tropics, although extensive data are not available. In Zambia, for example, the National Council for Scientific Research (NCSR, 1970) noted that infertility is one of the major problems confronting the cattle industry, but that the extent and causes were still obscure. Although it was believed that up to 40% of local cattle were infertile, no systematic studies had been undertaken at that time. Details are given below of some of the common causes of infertility.

5.1 Congenital morphological causes

Congenital causes of infertility are often inherited. They include developmental abnormalities of the ovaries, oviducts, uterus, cervix, vagina and vulva. Some are lethal, a few have a morphological significance and others a functional significance. Common morphological conditions include ovarian (gonadal) hypoplasia and aplasia, anomalies of the tubular genitalia, hermaphroditism, freemartinism, arrested development of the Mullerian ducts (White heifer disease) and double cervix (Lagerlof, 1963). Many of these abnormalities have been documented in zebu cattle by Perkins et al (1954), Kodagali (1974), Chenna (1980) and Kumi-Diaka et al (1981). However, they are of little significance if an appropriate culling programme is practiced.

Among 5238 non-pregnant slaughter cattle studied in Brazil, 17.27% had abnormalities of the ovaries and other reproductive tract segments, including agenesis, atrophy, hypoplasia and tumours (Vale et al, 1984). Segmental aplasia of the Fallopian tubes and uterus, abnormalities of the cervix and remnants of the Mullerian ducts were also observed by Basile and Megale (1974) among 6054 cows and heifers in southern America. Fifty had abnormalities of the hymen. Kumi-Diaka et al (1981) found anoestrus and genital abnormalities in 22.7% of 3000 cows in Nigeria, including ovarian hypoplasia in 13 cows and freemartinism in two. A 9.7% incidence of hypoplasia was found among 889 cows examined over 6 years in Southern Kartanaka, India (Hussein and Muniraju, 1984).

Bovine gonadal hypoplasia is not easy to diagnose (Lagerlof, 1963) and in cases of bilateral ovarian hypoplasia heifers do not develop secondary sexual characteristics. They are anoestrus and infertile. Where the condition is unilateral, normal sexual organs and oestrous activity may be observed. Such animals are fertile, although less so than normal. The condition is potentiated by an autosomal recessive gene with incomplete penetrance, and therefore the incidence of gonadal hypoplasia can be reduced by using only animals (both male and female) with normally developed sexual organs as breeding stock.

5.2 Functional causes of infertility and repeat breeding


5.2.1 Cystic ovaries and retained (persistent) corpora lutea
5.2.2 Other causes of anoestrus
5.2.3 Repeat breeders


In a sample of 510 Gir cattle in India, functional abnormalities were responsible for 59.4% of the cases of reproductive disturbance, compared with 23.3% attributed to pathological causes, 8.8% to anatomical factors and 4 8% to old age (senility) (Kodagali, 1974). The causes of functional infertility included cystic and inactive ovaries with anoestrus, early embryonic mortality with repeat breeding, and prolonged gestation. Anoestrus often reflects a hormonal disturbance and accounted for 47.8% of the cases. Repeat breeding, where cows require three or more services to conceive, accounted for 11.5% of cases. Singh et al (1981) also found functional infertility to be more common than infertility due to infectious diseases (76 vs 24%).

5.2.1 Cystic ovaries and retained (persistent) corpora lutea

Cystic ovaries contain one or more persistent fluid-filled cavities larger than a ripe follicle (Arthur, 1964). This is sometimes referred to as cystic ovarian disease (Chauhan et al, 1984). Ovarian cysts can be classified as follicular and luteal. They may vary in size from that of a ripe follicle to that of an orange. Their effects also vary according to their number and degree of luteinisation. Many unluteinised follicles tend to lead to nymphomania with frequent, irregular heats, whereas a cow with a few extensively luteinised cysts may become anoestrous. Cows with long-term cysts may show virilism. In addition to the pathologic follicular and luteal cysts, there are the non-pathologic cystic corpora lutea. These are normal structures that follow a normal ovulation but have a fluid-filled central cavity 7-10 mm in diameter. On rectal palpation they feel like normal corpora lutea but more fluctuant and soft. They do not alter the oestrous cycle duration and when conception occurs, it can be maintained to term (Roberts, 1971). The term "cystic ovaries" is therefore usually applied to pathological follicular and luteal cysts.

Estimates of the incidence of cystic ovaries in zebu cattle range from 1 to 13% (Rao et al, 1965; Kumi-Diaka et al, 1981; Pandey et al, 1982; Hussain and Muniraju, 1984). Osmanu (1979) found that in the 26% of cows surveyed in Ghana that were infertile, the single most important cause was cystic ovaries. Kaikini et al (1983) found the right ovary to be affected more (5.1%) than the left (1.2%) and only in 0.5% of cases were both ovaries affected simultaneously. The above are interesting observations since cystic ovaries have seldom been reported among taurine beef cattle or zebu cattle.

Cystic ovaries are conventionally diagnosed by rectal palpation, but it may be difficult to differentiate between follicular and luteal cysts. Although both tend to be smooth and convex, follicular cysts are more tense and thinner-walled.

Events in the hypothalamus, anterior pituitary, adrenals, ovaries and other target organs appear to be involved in the development of cystic follicles (Vandeplassche, 1982). There seems to be a break in the secretion of gonadotrophic-releasing hormone by the hypothalamus, which increases the ratio of follicle-stimulating hormone (FSH) to luteinising hormone (LH) in circulation. Insufficient LH results in failure to ovulate and no corpus luteum develops. Both follicular and luteal cysts are thus anovulatory, in contrast to the ovulatory cystic corpus luteum.

There appears to be a genetic predesposition to cystic ovaries. Estimates of the heritability of cystic ovaries range from 0.05 to 0.43 (Casida and Chapman, 1951; Erb et al, 1959; Johannson, 1960).

The incidence of cystic ovaries also appears to be related to milk yield in dairy cattle. Animals of all ages are susceptible, but incidence is greater in cows during their fifth or sixth lactation, i.e. when milk yield is often greatest. The condition is also commonly diagnosed 1-4 months after calving. It is thus suspected that lactation stress is a predisposing factor. Menge et al (1962) reported a genetic correlation of 0.22 between milk production and cystic ovaries, but Casida and Chapman (1951) found no correlation between the two factors. Hernendez-Ledezma et al (1984) observed that the incidence of cystic ovaries increased from 8.4% in primiparous cows to 25.9% in cows in their fifth lactation. The incidence overall was also higher in cows with metritis (14.6%) and those with retained placenta (13.6%) than in healthy cows (8.5%). Other factors influencing incidence were prolonged interval from calving to first detected oestrus, first mating and conception, and the interval from first detected heat to conception.

Vandeplassche (1982) indicated that a close association may develop between cystic cows (the bullers) and certain herdmates and that this increases the likelihood of the "chosen friends" becoming cystic. He also noted that treating cows with small dose of oestradiol benzoate may induce cystic ovaries.

Forage legumes are often advocated as a means of improving animal nutrition in the tropics. Some, however, contain substances, such as phytoestrogens, that may reduce fertility. Feeding cows for prolonged periods on clover, lucerne (alfalfa), or other plants rich in phytoestrogens may lead to cystic ovaries. Little (1976) assessed several pasture species, particularly tropical legumes, for oestrogenic activity and found that lucerne (Medicago sativa) had a slight oestrogenic potential. More evidence is needed on the oestrogenic effects of forage legumes, especially where they form an important component of natural pastures.

As noted above, cows with cystic ovaries can show either nymphomania or anoestrus. Nymphomaniac cows exhibit prolonged periods of frequent oestruses. They mount others and stand for mounting, even by a bull. In contrast, cows with virilism mount others but do not stand for mounting. Nymphomaniac cows have been called "bullers" because of these homosexual tendencies. They develop oedema of the vulva, copious mucous discharges may be seen and the sacro-sciatic ligament frequently sinks, causing the coccyx to tilt up.

Follicular cysts are follicle-like structures more than 2.5 cm in diameter that persist on the surface of the ovary for more than 10 days (Roberts, 1971). They grow in a disorderly manner, fail to regress or undergo atresia and instead accumulate fluid. Since there is no ovulation, such cows are infertile until normal cycles resume.

Follicular cysts during the early postpartum period may regress by themselves but several therapeutic approaches have also been tried. Products with high LH activity have long been used to treat follicular cysts, to good effect (e.g. Casida et al, 1944; Roberts, 1955; Elmore et al, 1975). Seventy to 80% recovery rates have been recorded, although subsequent first service conception rates tended to be low. Progestational compounds have also been used, but their efficacy is still in doubt. LH-rich products administered in conjunction with progesterone compounds have given better results than either product alone. More recently gonadotrophic-releasing hormone (GnRH) or its analogues have been used to induce LH release; this initiated oestrus in about 80% of the animals (Kesler and Garverick, 1982) due to the induced preovulatory-like LH surge which might otherwise have been insufficient for normal ovulation and corpus luteum formation to take place. The interval from GnRH treatment to oestrus may be shortened by 18 to 24 days by injecting prostaglandin F2 a (PGF2 a) 9 days after GnRH.

Care should be exercised when administering prostaglandins to cattle. Local haemorrhages have been observed at prostaglandin injection sites due to prostaglandins other than PGF2 a in some products. Large abscesses may develop at these sites due to anaerobic Clostridia spp. bacteria, introduced by unsterilised needles. Therefore, clean needles should be used for PGF2 a injections, or an antibiotic (e.g., 1 ml streptomycin) should be added to the PGF2 a dose.

When ovaries are undergoing cystic degeneration, the walls of the growing cystic follicle may degenerate. Oocyte development is terminated and about a third of the cysts may luteinise. Luteal cysts are thus less frequent than follicular cysts. Careful diagnosis is needed to differentiate them from cystic corpora lutea, which are not pathological. Luteal cysts have a larger antrum surrounded by several layers of luteal cells, which continuously elaborate progesterone, rendering the cow anoestrous. Continuously high progesterone levels may therefore be indicative of luteal cysts.

Pressure can be applied to luteal cysts to rupture them and express their lining (Arthur, 1964), but recovery rates tend to be low. Ovulation can also be induced by administering luteinising hormone (human chorionic gonadotrophin: hCG) or 0.5-1.0 mg GnRH (Vandeplassche, 1982). Most cows show oestrus 18 to 23 days after GnRH therapy. The interval from GnRH administration to oestrus can be shortened to 12 days by administering prostaglandins 9 days after GnRH (Kesler et al, 1978). Bovine luteal cysts are difficult to differentiate from follicular cysts and this may be the reason that PGF2 a therapy is often ineffective.

GnRH has also been used prophylactically to reduce the incidence of ovarian cysts. Administering the hormone 8 to 23 days (Britt et al, 1977) and 12 to 14 days (Zaeid et al, 1980) after calving was found to reduce the number of cows that developed ovarian cysts or were culled for infertility.

Finally, reference has sometimes been made to retained or persistent corpora lutea, i.e. those that persist beyond the normal luteal phase. These continue to produce enough progesterone to prevent further follicular development, ovulation and oestrus. Severe endometritis may be associated with a persistent corpus luteum due to toxic damage to the endometrium, which prevents proper secretion of luteolytic prostaglandins. This can also occur with pyometra, foetal mummification and maceration, i.e. conditions that simulate pregnancy (Boyd, 1977). Lamming (1977) reported persistent corpus luteum to be rare (under 2%) in cows with normal uteri.

Diagnosis of persistent corpus luteum is based on the presence of a large, persistent corpus luteum on the ovary, anoestrus and persistently high levels of progesterone. Frequent visits and rectal palpations of affected cows, with accurate records of the rectal findings at each visit, are required before a diagnosis of persistent corpus luteum can be confirmed. Once confirmed, the persistent corpus luteum can be enucleated or lysed by prostaglandins.

5.2.2 Other causes of anoestrus

Anoestrous cows have small, flaccid uteri and small, inactive ovaries with no palpable corpus luteum or follicle. In contrast, cycling cows are identified by the size and tone of the uterus and the presence of the corpus luteum or follicle or both on either of the ovaries. Nevertheless, cows may show anoestrus despite having normal ovarian structures.

Anoestrus is a major problem in the tropics and subtropics, where inadequate nutrition, high ambient temperature, high parasite burdens and disease exacerbate the problem. Low body weight and poor body condition, compounded with lactation stress, can further extend the postpartum anoestrous period. Vandeplassche (1982) indicated that the long anoestrous period in the nursing cow might be due to an elevated level of prolactin, which appears to depress the secretion and release of GnRH, or that the pituitary may be less responsive to GnRH during nursing. Since the anoestrous period tends to be longer and more common among first-calf heifers, the author also suggested that immaturity could be a contributing factor. Although the ovaries of such cows may not be completely inactive, reduction in oestrogen secretion over long periods may result in underdevelopment of other genital organs. The vagina, uterus and ovaries of these animals feel inactive on rectal palpation. Blood or milk progesterone levels are also low.

Conditions that simulate pregnancy, such as pyometra (pyometron), severe metritis, foetal maceration or mummification, may cause anoestrus. Pyometra, which often occurs when foetal membranes are retained or following postpartum metritis, is a frequent cause of anoestrus. These conditions damage the endometrial lining of the uterus and reduce secretion of luteolytic prostaglandin. The cyclic activity of the ovary is thus interrupted in the luteal phase and the cow or heifer is anoestrous until the condition is corrected. Without regular veterinary care and palpation, these conditions may remain undiagnosed and the cow may be believed to be pregnant.

Although anoestrus can, to some degree, be overcome by treatment, it is more practical to ensure that animals are well managed and are fed to maintain good condition during critical periods, i.e. prior to mating and during lactation, in order to avoid anoestrus.

Anoestrus is normal in pregnant, prepubertal and recently-calved animals. Pregnancy is a common cause of anoestrus, but this is often overlooked where service records are poor. Since many treatments for anoestrus terminate pregnancy, the possibility that cows presented as anoestrous are pregnant should be eliminated before treatment begins.

5.2.3 Repeat breeders

Repeat breeders are those cows that require three or more services to conceive (Enkhia et al, 1983; Casagrande and Goes, 1977). Kaikini et al (1983) estimated the incidence of repeat breeding to be 21.9% in 411 Holstein x Gir cross cows studied at Rahuri, India, between 1972 and 1980. Nuru and Dennis (1976) found that the incidence of repeat breeding ranged from 16.6 to 58.8% in Fulani herds surveyed in six states of northern Nigeria in 1972-73. Singh et al (1983) reported a range from 7.4 to 18.6% among Holstein, Danish Red and Sahiwal cows and their crosses.

Repeat breeding can be caused by a number of factors, including subfertile bulls, endocrine problems, malnutrition, reproductive tract infections and poor management. Vandeplassche (1982) cited previous work in which adhesions of the ovarian bursa, salpingitis, cystic ovaries and endometritis were found in repeat-breeding cows. Bhatt et al (1979) found antibodies to seminal antigen in the genital secretions of 12 repeat-breeding cows in Bikaner, India. Munoz de Cote et al (1980) made a similar observation in Mexico; 32 out of 50 infertile Holstein cows had antibodies, at a titre of 1.8 or more, to Holstein bull spermatozoa while none of 50 fertile heifers had a titre higher than 1.8. Thirty of the "infertile" Holstein cows conceived when inseminated with zebu semen, whereas only 7 of the "infertile" cows inseminated with Holstein semen conceived. Proper diagnosis of the cause of repeat breeding is very important and requires a careful assessment of production and breeding records.

Repeat breeding can be treated by enucleating the corpus luteum or causing its lysis by prostaglandins, uterine massage or manual stimulation of the clitoris after artificial insemination or infusion of the uterus with 50-200 ml of 1 to 5% Lugol's iodine, which has a stimulating effect on the uterus. Enucleation of the corpus luteum may cause adhesions between the ovary, bursa and fimbria or haemorrhage in the ovary. Pharmacological enucleation with prostaglandins avoids this problem. Intra-uterine infusion of antibiotics has been used but there is little evidence that this increases fertility during the following cycle. However, fertility tends to increase by the second or third heat after treatment. Human chorionic gonadotrophin can be administered at the time of AI to promote ovulation or progesterone can be injected 4 to 5 days after service. Details are given in the following sections on how pathological causes can be handled.

5.3 Infectious causes of infertility


5.3.1 Bacterial and protozoan infections
5.3.2 Viral infections
5.3.3 Mycoplasmas
5.3.4 Endometritis, metritis and pyometra, and the use of prostaglandins in postpartum uterine pathology
5.3.5 Retained afterbirth


Infectious agents that have a detectable effect on the animal may interfere, if only slightly, with its reproduction. These include several bacterial, protozoan, viral and mycoplasmal infections. Details of the most common and economically important ones are given below. Several are important zoonoses. Some details on endometritis, metritis, pyometra and retained afterbirth are also given.

5.3.1 Bacterial and protozoan infections

Pathological lesions were observed in the reproductive tracts of 55.14% of 700 cows examined at post-mortem on two ranches in Shaba, Zaire (Binemo-Madi and Mposhy, 1982). Most of these were on the ovary and salphinx. They may have been caused by abnormal rectal manipulations or bacterial infections of the uterus, vagina and vestibulae. About 45% of the cows were still capable of breeding, indicating that pathological conditions do not necessarily render cows permanently sterile. Their seriousness depends on the location of the infection.

5.3.1.1 Brucellosis

Importance and incidence

Brucellosis is found world-wide. It affects humans, domestic animals and wildlife. It is caused by Brucella abortus, B. melitensis, B. suis, B. ovis and B. canis.

De et al (1982), in a study of 989 cows in West Bengal, attributed abnormal termination of pregnancy, cervicitis, endometritis, repeat breeding and anoestrus to brucellosis, campylobacteriosis, leptospirosis and trichomoniasis. Rao et al (1977), Hussain and Muniraju (1984) and Kaikini et al (1983) noted that these, and other infections, can lead to inflammation with bursar and uterine adhesions, periglandular fibrosis, hydro- and pyo-salphinx, hydrometra, pyometra, endometritis, vaginitis, and metritis. Other effects include early embryonic loss and repeat breeding, abortion, dystocia, retained membranes, stillbirth, and prolapse in late gestation.

Brucellosis has been extensively studied, partly because it causes widespread economic losses due to abortion and extended calving intervals and because it affects humans.

Many countries in the temperate regions have substantially reduced the incidence of brucellosis. Some, such as Denmark, UK, The Netherlands and Romania, have eradicated the disease, mainly through rigorous test and slaughter policies. The diagnosis of brucellosis is now well standardised and, in general, highly efficient. However, the disease is still prevalent in many countries, especially in the tropics.

The reported incidence of brucellosis in Africa varies from zero to 100% (Chukwu, 1985; 1987). Some of the variation can be attributed to sampling technique, the herds sampled and the diagnostic tests used. Some cows also only react positively to serological tests when pregnant. Therefore, one must be cautious in interpreting incidences across countries or among herds.

A survey of cattle on the Accra plains in Ghana indicated an incidence of 20-30%, with high rates of abortion and stillbirth (Oppong, 1966). Esoruoso (1974) reported that up to 60% of breeding cows and heifers in western Nigeria were infected with Brucella abortus. In Ethiopia, Meyer (1980) found that 39% of the cattle belonging to the Institute of Agricultural Research (JAR) were serologically positive for brucellosis in 1978, compared with 18.1% in 1975. A comparatively low incidence of 0.25% was reported in Malawi by Klastrup and Halliwell (1977). Studies on brucellosis in Africa are reported by Dafalla (1962), Mustafa and Nur (1968) and Mustafa et al (1976) in Sudan; Waghela (1976) in Kenya; Kagumba and Nandhoka (1978) in Uganda, Kenya and Tanzania; Marinov and Boehnel (1976) in Tanzania, and Wernery et al (1979) in Somalia. These, and reports by Chukwu (1985; 1987), Vandeplassche (1982), Blood et al (1979), Arthur (1964), Roberts (1971) and Tekelye Bekele et al (1989a), are drawn on subsequently.

Transmission

Brucellosis is normally acquired by cattle by ingesting the bacteria. Infection may also occur through the mucosa of the eye, nose and teat, and through the endometrium if the cow is artificially inseminated with infected semen. The multi-layered mucosa of the vagina seems to protect against infection following natural service.

The disease is most serious in cows infected during pregnancy. The bacteria show a preference for the pregnant uterus, foetus and the lymph glands of the udder. Both the membranes and foetus respond to Brucella infection by increasing their production of erythritol, a simple carbohydrate, which increases the growth rate of the bacteria. This usually results in abortion at about 6 to 8 months of gestation. The organism may also produce toxins and allergens, cause vascular thrombosis, increase uterine motility, and disturb production of sex steroids and prostaglandins, contributing to abortion (Vandeplassche, 1982). In some cases the dead foetus is not aborted, but is retained in a mummified or macerated form. If a calf is born alive it is likely to be weak and to contract calf scours easily. Many die soon after delivery.

Aborting infected cows or heifers are a major source of infection for other cattle and people handling them. Aborted material and vaginal discharges from infected females are heavily infected with Brucella, and these contaminate pastures, pens and buildings. Organisms are also present in the milk of infected cows. Brucellosis is a professional hazard for cattle keepers and veterinarians.

Foetal membranes are commonly retained because of uterine inertia, placentitis or both. Retained membranes must be handled with great care. Puerperal metritis may develop and cows may remain infertile for some time.

After abortion, uterine infection normally declines within a month. The animal may not abort on the next conception, but she will continue to discharge the Brucella. Some calves are born infected. Many lose the infection quickly but a few do not. The latter do not show any signs of the disease and represent "latent infection". The organism remains dormant until the animal becomes pregnant. Calves born to serologically positive dams are, therefore, at risk of developing the disease in the future and ought to be carefully screened when pregnant. Udder (Alton, 1981) and milk infection lasts several months or years and may be the source of uterine infection during subsequent pregnancies.

Diagnosis

Brucellosis should be suspected whenever a cow aborts unexpectedly, except in a Brucella-free herd. Confirmation requires bacteriological examination, culture of the organism or serodiagnosis.

A smear from the necrotic surface of placental cotyledons, stained with 20% fuchsin, 3% acetic acid and 10% methylene blue, can assist the first tentative diagnosis of brucellosis. The Brucellae stain red against a blue background. Chlamydiae may also stain red but are smaller and primarily intracellular (Vandeplassche, 1982).

The bacteria are rarely cultured, partly because diagnostic material, particularly foetuses, usually reaches the laboratory in a condition unsuitable for proper examination. Serological tests are, therefore, commonly employed. However, the various tests used differ in convenience and accuracy. A good serological test would establish early diagnosis, identify chronic infections, and distinguish between the antibodies of vaccination and infection (Fensterbank, 1986).

In the milk ring test (MRT), also called the Bang Ring Test, a drop of haematoxylin-stained antigen is added to 1 ml of milk. This is incubated at 37°C for half to 1 hour. This test is widely used, fairly efficient, economical and easy to perform. A positive result is shown by the development of a clump of stained organisms deposited in a ring on the surface of the preparation. The negative result is bluish milk covered by an uncoloured layer of cream. However, the sensitivity and specificity of this test are low, and test results can even vary for the same animal at different periods. It is therefore used only for quick screening or surveillance of milk samples. Milk should be tested monthly. To reduce the chances for misdiagnosis, such as can arise after Strain 19 vaccination or due to the presence of certain milk proteins in late lactation, test milk can be diluted 5 to 10 times with normal (Brucella-free) milk.

In the spot agglutination test, developed in the United States (Alton, 1981), a drop each of serum and antigen are mixed on a card or on a plastic, ceramic or glass plate. This is also known as the Rose Bengal Test (RBT) or rapid plate agglutination test. RBT is performed on serum using stained antigen at pH 3.6. It is economical, simple to perform and gives results in 4 minutes. Like the MRT, it is used as a quick screening test. A positive result is indicated by clear agglutination. To aid judgement, a known positive sample is run at the same time for comparison.

More sensitive and specific tests include the complement fixation test (CFT), which detects IgG1 and IgM antibodies (Fensterbank, 1986). This is the most accurate and sensitive test for brucellosis and distinguishes between antibodies of infection and vaccination. However, it must be performed by a trained technician.

The enzyme-linked immunosorbent assay (ELISA) has been used to diagnose brucellosis (Stemshorn et al, 1960), but has not been extensively adopted as a routine test. Diaz et al (1979) described a simple immuno-diffusion test that they thought could differentiate between infected and vaccinated animals. Kaneene et al (1979) reported that the level of immunity among vaccinated cattle could be assessed by exposing peripheral lymphocytes to Brucella antigen in vitro. They also indicated that this procedure could be used to diagnose the disease.

Control

Brucellosis can be controlled through strict hygiene in the handling of potentially infected material and by vaccinating all animals. To eradicate the disease, all infected animals must be slaughtered.

Cows, especially those that react positively to serological tests for brucellosis, should be isolated from the herd before calving and their calves monitored for latent infection. Pregnant animals should be observed for imminent abortion and all aborted material must be disposed of properly, e g by burning or deep burial. Farm labourers should be aware of the dangers of brucellosis and avoid spreading the disease.

Cattle should be bought only from Brucella-free herds. If this is not possible, animals should be tested serologically on the farm of origin prior to put-chase and again one month later after arrival on the new farm. They should be kept in quarantine until after the second test. If an animal reacts positively to the MRT or RBT tests, the result should be checked using the CFT test. If the latter is also positive, the animal should be slaughtered.

Where the incidence of brucellosis is high, calves should be vaccinated with the attenuated Strain 19 vaccine at 3 to 6 months old. Persistent antibody titres that may be hard to distinguish from infection, and infection of the udder, have been observed in heifers vaccinated at 8 months or older. Vaccinal titres tend to recede more rapidly when heifers are vaccinated at 6 months or younger (Carroll, 1972) and there is no difference in immunity levels of calves vaccinated at 3,4,6 or 8 months old (Mathei and Deyoe, 1970). Sexually mature animals can be vaccinated with the killed adjuvant vaccine 45/20. The vaccine is given twice, 6 weeks apart, followed by an annual booster. The resistance developed is similar to, but not better than, that from calfhood vaccination using Strain 19. Therefore, it is not advisable for heifers that received Strain 19 as calves.

Bulls should not be vaccinated. Strain 19 organisms have been isolated from the genitalia of vaccinated bulls (Lambert et al, 1964). These could infect their seminal vesicles, epididymides and testes. Bulls often stay in the herd for a short time, during which they do not transmit the organisms naturally. However, bulls at artificial insemination centres must be rigorously tested for the disease. Non-specific post-vaccination reactions to serum agglutination tests have also been observed among AI bulls. Bell (1984) believed that the cause could be an anomaly of the immune system, particularly of IgM.

Prevention of the disease in humans is contingent upon the control of the disease in animals. Once the incidence of the disease is substantially reduced by vaccination, a test and slaughter programme can be attempted to eliminate infected animals. Once a herd has been certified as being free of the disease, continuing vaccination may not be necessary but the herd must be kept closed.

5.3.1.2 Trichomoniasis

Incidence and transmission

About 40 years ago, trichomoniasis was an important cause of infertility in cattle in many countries. The disease causes endometritis, pyometra, abortion and sterility. It is a venereal disease spread at service or by artificial insemination with improperly treated or handled semen. It is sometimes called Bovine Venereal Trichomoniasis. Its incidence has been greatly reduced where artificial insemination is widely used, as in the UK, The Netherlands, France and Cyprus. It nonetheless remains a problem in other countries, especially in dairy cattle, poorly managed herds and herds which use communal bulls.

The incidence of trichomoniasis in Africa and the tropics is not widely reported, partly because diagnosis is complex and time-consuming. Consequently, it is not clear if the disease is widespread. De et al (1982) did not find infected animals among 13 well-managed herds in West Bengal, India. Only one cow from a rural herd was diagnosed as being infected. Klastrup and Halliwell (1977) also failed to demonstrate the disease among 294 slaughter bulls and 54 others maintained at breeding centres in Malawi. However, in Egypt, Gawade et al (1981) found an incidence of 4.6% among Holstein bulls, and in Nigeria Akinboade (1980) found an incidence of 14.9% among slaughter animals.

Trichomoniasis is caused by Trichomonas fetus, a protozoan about 15 m long with an undulating membrane. In bulls, the trichomonads normally colonise the crypts of the external mucous membrane of the penis and prepuce. Since these crypts are deeper in older bulls, the prevalence of the disease tends to increase with bull age. Infection does not induce any local antibodies or specific agglutinins in the blood of bulls. Bulls carry the disease for a long time without showing symptoms.

Cows and heifers that have never been exposed to the disease become infected following either natural service by a carrier bull or artificial inseminations with contaminated semen. Following natural service, the protozoa first multiply in the vagina and cervix for about 3 weeks. In about a quarter of the cows, the organisms do not migrate to the uterus. With intrauterine artificial insemination, the uterus is directly infected.

Importance

Trichomoniasis causes infertility, repeat breeding, delayed return to oestrus after mating, early embryonic death and, sometimes, abortion. It may directly cause the death of the embryo or may do so via uterine endometritis and marked leucocytic diapedesis into the endometrium (Vandeplassche, 1982). The affected cow returns to oestrus or may abort anytime from 2 to 7 months after conception. The foetus can degenerate. The corpus luteum may be maintained because the endometrium does not secrete luteolytic prostaglandins. Mucus accumulates, resulting in mucometra. Pus may eventually be observed, indicating pyometra. However, the parasite tends to attack the superficial layers of the endometrium and cow fertility usually returns to normal.

Affected cows develop agglutinating antibodies in their vaginal mucus. This, together with hormonal changes during subsequent oestrous cycles, tends to protect the cow during an infection but may not protect her from re-infection. Withdrawing infected cows from breeding for at least 3 months and subsequent use of clean bulls or artificial insemination can help control the disease.

Diagnosis

A low 60- to 90-day non-return rate, together with a large number of repeat-breeding cows and cows that exhibit purulent vaginal discharges, endometritis, abortion and pyometra, might indicate trichomoniasis. The symptoms of trichomoniasis and campylobacteriosis are similar. Both lead to irregular inter-oestrous intervals. They are best differentiated by isolating the causative agents.

Initially, preputial washings, semen or smegma from bulls should be examined microscopically for the presence of trichomonads. For preputial washings, about 50-100 ml of physiological saline is introduced into the prepuce under gravity or from a syringe and tube. The prepuce is closed and agitated vigorously for 2 to 3 minutes to free any organisms present in the crypts of the penis and prepuce mucous membrane. The fluid is collected, centrifuged and the supernatant discarded. The residual is shaken and a drop examined at 100x magnification, preferably with a cover-slip, at 37°C on a warm slide stage. To collect preputial secretions (smegma), a dry plastic uterine infusion pipette attached to a 12-ml syringe is introduced into the fornix of the unprepared sheath, the syringe is opened to 10 ml and the pipette is moved back and forth. About 0.2 to 1.0 ml of smegma can be obtained which is rinsed into 3 ml of physiological saline.

Cervical and vaginal mucus can also be examined but this is only really useful during the first few weeks of infection. Thereafter, the motility of the trichomonads diminishes and only the undulating membrane can be discerned at 250x magnification. In the case of an abortion, microscopic examination of foetal fluids, placental secretions and foetal abomasal contents can be useful.

Isolation of even one trichomonad, from either the cow or the bull, confirms diagnosis. Only few trichomonads may be present and, if the disease is suspected, a second sample should be taken if no trichomonad is found in the first. Samples should be examined within 6 hours of sampling as the parasite tends to die within 6 hours of leaving the animal's body. At temperatures lower than 37°C the undulation of the parasite tends to slow or stop. Thus techniques suitable for field studies in the tropics need to be developed.

As an alternative to direct examination, preputial washings or purulent discharges can be cultured, preferably within 6 hours of sampling. Immediate inoculation onto specific culture media is advisable. Where this is not possible, especially under field conditions, transport media may be used.

Buffered saline solution with foetal bovine serum, and lactated Ringer's solution are simple and effective transport media. Vandeplassche (1982) suggested Difco-Lash medium (No. D-1016T), and Oxoid medium as culture media. Klastrup and Halliwell (1977) referred to two trichomoniasis culture media, one with and one without antibiotic, while De et al (1982) used Douglas' broth and glucose broth serum medium. Both direct examination and culture methods can take time to yield results. Sero-diagnostic procedures are generally unsatisfactory.

Treatment and control

Treatment of infected cows with vaginal antiseptics has not been very successful. In animals with pyometra, it is better to enucleate the corpus luteum or to lyse it with prostaglandins. Treatment may be repeated 10 or 11 days later.

Trichomoniasis is a "self-limiting" disease in the non-pregnant cow with an involuted uterus. After being sexually rested for 3 or 5 cycles, many cows develop some immunity and their fertility improves. Only clean bulls or semen should be used for breeding and cows with abnormal genital tracts should be culled.

"Carrier" bulls and sexually active oxen can re-infect treated, recovered and susceptible females and should therefore be culled. Carrier bulls can be treated, but treatment is lengthy and should not be considered unless the bull is very valuable.

The antibacterial agents used by artificial insemination centres to preserve semen do not control trichomonads. AI centres must therefore test their bulls regularly to ensure that they are not infected. Young bulls chosen as breeders should not be allowed in contact with untested teaser cows. Both teaser animals and bulls should be selected from disease-free herds whenever possible and held in quarantine prior to puberty and collection.

5.3.1.3 Campylobacteriosis

Incidence

Abortion in cattle and sheep was first associated with vibrionic organisms in 1918 by McFadyean and Stockman (cited by Laing, 1963). The organisms were first named Vibrio fetus by Smith (1918), and later Campylobacter species.

The species most commonly encountered in the bovine genital tract are Campylobacter fetus subsp. venerealis serotype A, C. fetus subsp. fetus serotype A and C. fetus subsp. fetus serotype B. Of these, infertility in cattle is most often associated with C. f venerealis A (90%) and C. f. fetus B (10%) and only rarely C. f. fetus A and B (Vandeplassche, 1982).

The incidence of campylobacteriosis in the tropics varies. De et al (1982) found an incidence of 6.1% among 194 cows sampled on 13 well-managed farms in West Bengal, India. None of 295 cows from individual rural farms was affected. In Malawi, the incidence reported by Klastrup and Halliwell (1977) was 11.5% in 294 zebu and 11.1% of 54 exotic bulls tested serologically. When the vaginal mucus agglutination test was performed on the cows, it showed that 53.8% of the herds and 13.4% of the samples were infected. Using the same test in Zimbabwe, 33% of the cows sampled were found to be positive (Terblanche, 1979).

Transmission and pathogenesis

Campylobacteriosis is a venereal disease and although transmission via fomites and between bulls has been suggested, this is unlikely. Garcia et al (1983) stated that transmission is purely venereal or via artificial insemination, and that attempts to infect cattle by vulval contamination failed. Clark (1971) indicated that direct transmission of infection between cows probably does not occur naturally.

Events subsequent to infection are similar to those described for trichomoniasis except that the migration of the organisms from the vagina and cervix appears faster. In cows, infection is initially acute but eventually becomes chronic. Acute infection is associated with infertility and the chronic phase with abortion, although abortion may also occur in the acute stage (Garcia et al, 1983). Catarrhal vaginitis in the acute phase results in an increased production of clear, cloudy or muco-purulent discharge for 3 to 4 months. Catarrhal cervicitis may result in a reddening of the cervix. Once in the uterus, the infection flourishes, causing a low grade inflammation, and results in infertility lasting about 6 months (ABS, 1972). Abortion may occur at any time but usually occurs 5 to 6 months after endometritis and placentitis have occurred. The incidence of abortion can be over 5%. Foetal membranes are extensively affected. The intercotyledonary areas are covered by dark brown purulent material. The animal may recover spontaneously after 2 or 3 months despite the continued presence of the bacteria in the vagina. The bacteria may migrate into the oviducts and cause more permanent infertility due to salpingitis.

Ordinarily a large number of cows in a herd get infected from the same bull or improperly prepared semen. The bull is always a symptomless carrier; its genitals and semen appear normal. The inflammation in the female is low grade and diagnosis based on clinical signs may be difficult in the acute stage. Breeding records often give the first indication, with many cows returning to oestrus after repeated service: the repeat breeder syndrome (Table 25). Oestrous cycles are longer than normal, usually more than a month (Clark, 1971), indicating early embryonic death. After variable periods of infertility many cows recover and regain normal fertility. Thus, as with trichomoniasis, infected females should be sexually rested.

Infected cows develop local antibodies (IgG, IgM, IgA) in their genital tract mucus (Vandeplassche, 1982, citing work by others). The IgA antibodies may persist in the vaginal/cervical region for over 10 months. The antibodies that develop in the uterus are dominated by the IgG type (Vandeplassche, 1982), which results in rapid phagocytosis of C. fetus and recovery of the uterus in about 2 months. However, animals that recover may be less fertile than normal. The fertility of the herd will remain low as long as susceptible heifers and cows are present and infected bulls are used.

Diagnosis

Breeding records showing low non-return rates, many repeat breeders and a high incidence of abortion at mid-term suggest campylobacteriosis. Isolation of C. fetus from the bull or cows will confirm the diagnosis.

Campylobacteae can be isolated from the genital secretions (sheath washings or semen) of bulls. Hoerlein (1970) gives a detailed account of laboratory diagnosis of campylobacteriosis. Garcia et al (1983) indicate that the Bartlett technique for collecting preputial material using an AI pipette remains widely used. They cite Dufty and McEntee (1969), who showed that the aspiration method is more effective than preputial washing for recovering C. fetus, and Tedesco et al (1977), who observed that scraping the preputial and penile mucosa was superior to aspiration and washing methods. Special buffered saline should be used for washings (Vandeplassche, 1982). Various media have been recommended for initial isolation; Laing (1963) and Dufty and McEntee (1969) should be consulted for detail and to decide on which medium is most suitable for work in different locations.

Table 25. Comparison of the number of services per pregnancy in non-infected and Campylobacter-infected heifers

Service on which conception occurred

Infected heifers (101)

Non-infected heifers (108)

1

5

54

2

8

32

3

10

11

4

12

3

5

17

3

6

12

2

7

6

2

8

6

0

9

1

0

10

2

0

11

1

0

12

2

0

Total

82

107

Source: Laing (1960).

Samples should be inoculated onto isolation media within 6 hours of sample collection. Where this is not possible, transport media should be used. Campylobacteae are difficult to culture and the immunofluorescent antibody (IFA) or fluorescent antibody (FAT) test is more convenient. At present the technique is specific for C. fetus but cannot differentiate between subspecies. Samples can be kept refrigerated for several days and still yield reliable results with this test. Using culture and FAT together gives results approaching 100% reliability. Where good selective media can be prepared the two methods make the virgin heifer test, whereby the suspect bull is test-mated to clean heifers, unnecessary.

A direct Gram-stain smear of an aborted foetus, placenta or foetal stomach may reveal the short "S" shaped organisms sometimes called "flying seagulls". Culture and FAT tests may then follow. Vaginal mucus can also be used for diagnosing campylobacteriosis. A vaginal mucus agglutination (VMA) test will indicate infection in a herd but does not reliably indicate infection in individual animals (Hughes, 1953) since the specific agglutinins (IgA) are only found in 50% of infected animals (Garcia et al, 1983). Mucus can be collected by aspiration using a glass or plastic AI pipette (Schurig et al, 1973). For serological purposes mucus may be recovered by a sponge tampon attached to a plunger (Hughes, 1953; Laing, 1963).

If samples are to be used in an effort to culture the organism they must be free of contamination and oxygen tension must be minimised to ensure the survival of C. fetus. This can be achieved with AI tubes that can be sealed immediately or by storing samples in sealed tubes and shipping them at -70°C in dry ice. Alternatively, transport media can be used. The transport enrichment medium (TEM), after Clark and Dufty (1978), is useful in isolating C. fetus venerealis. It comprises solidified bovine serum with antibiotics. Organisms can be isolated from TEM kept at 22 to 23°C for 2 days using inocula as small as 100 organisms. The major advantage of TEM is that field samples can be shipped unrefrigerated to the laboratory. Other transport media, based on thioglycollate, cooked meat or veal infusion broth with charcoal powder, have been reported (Foley et al, 1979; de Lisle et al, 1982).

Treatment and control

Treatment should aim to cure the infected bull. Fat-free cream containing 1% neomycin or polymixin can be applied to the penis and prepuce under sedation. Streptomycin (Seger et al, 1966) or erythromycin have also been used, but both have been associated with false cure in bulls and cows. Cows can also be treated by infusing streptomycin or erythromycin into the uterus but this does not clear organisms in the vagina and cervix and the cow can be re-infected.

Infection with C. fetus does not induce immunity in bulls. Therefore, bulls can be re-infected after treatment. A curative treatment based on two doses of 50 mg C. f. venerealis (dry weight), 4 weeks apart, has been reported to overcome this problem (Vandeplassche, 1982). This can be coupled with infusion of antibiotic into the prepuce, intramuscular injection of streptomycin or intravenous injection of erythromycin to produce a cure that has little effect on semen production. A booster vaccine is necessary every year for cows (Carroll, 1972) to eliminate the disease from the herd. Table 26 shows the increase in fertility resulting from vaccination.

Table 26. Effect of inoculation with commercially prepared attenuated Campylobacter fetus infected herds

Experimental herd

Vaccinated

Non-vaccinated

No

% pregnant

No

% pregnant

H96 South-east Colorado

1 year heifers

70

83

53

39

2 year cows

32

66

29

38

H98 North-east Nebraska

1 year heifers

26

81

23

43

H106 Central Colorado

1 and 2 year olds

7

100

6

50

H107 North-east Colorado

1 year heifers

147

48

150

8

Source: Hoerlein et al (1965).

Although control of the disease centres around preventing the introduction and spread of infection, this may be difficult in herds that use a communal bull. If more than one bull runs with the herd, it may be difficult to determine which bulls are infected. Artificial insemination with semen from uninfected bulls is thus one of the best ways to control the disease (Roberts, 1971). Where this is not feasible, sexual rest of affected females combined with vaccination may be the best approach.

5.3.1.4 Leptospirosis

Importance and transmission

Bovine leptospirosis is a systemic disease characterised by fever and, sometimes, mastitis and abortion. Leptospirosis should be suspected when abortion occurs in cows showing other symptoms such as icterus and haemoglobinuria (Carroll, 1973). It is one of the most widespread zoonoses.

Leptospirosis has not been extensively researched in Africa. Moch et al (1975), working in Ethiopia, found incidences of 91.2% in horses, 70.7% in COWS, 57.1% in pigs, 47.3% in goats, 43.4% in sheep, 15.4% in camels and 8.3% in dogs. Ball (1966) reported incidences of 34% in cattle and 9.3% in goats sampled in Kenya and Uganda.

The disease is caused by Leptospira bacteria. These are spirochaetes. Some 120 Leptospira serotypes have been identified by the World Health Organization (Moch et al, 1975). The serotypes associated with bovine abortion are Leptospira pomona, L. canicola, L. australia, L. icterohaemorrhagica and L. grippotyphosa. They are all sensitive to antiseptics and desiccation and their virulence and pathogenicity are highly variable. Lawson (1963) indicated that L. pomona is the serotype most commonly implicated in bovine abortion.

Animals infected with Leptospira excrete the bacteria in their urine. Direct or indirect contact with the urine of infected animals is the major route of infection in both animals and man. The usual route of infection is via the digestive tract, but the disease may be contracted via the respiratory and reproductive tracts, eyes or skin. In cows, infection is often followed by pyrexia and reduced milk production.

In the pregnant cow the organisms show an attraction for the uterus and attack the foetus or endometrial capillaries. This may result in abortion during the last trimester or the birth of a weak or dead calf. Aborted foetuses show no characteristic lesions other than subcutaneous oedema and fluid-filled cavities. Foetal membranes may be retained, sometimes causing metritis and infertility. The organisms also settle in the kidneys and in 2 or 3 weeks leptospiruria starts. If the bacteria invade the udder they may cause mastitis or agalactia. The udder is flaccid and milk becomes thick, yellow and clotted.

Antibody titres in the blood of infected cows are elevated after an initial temperature rise. The titres vary from 1: 400 to 1: 1000 depending on the serotype. Antibodies can disappear after 2 months. As a result, cows may continue to excrete the organisms in their urine.

Diagnosis

Leptospirosis should be suspected following abortion associated with acute illness and the presence of blood in the milk for some days. However, leptospirosis can cause abortion without giving any other obvious symptoms (Stoenner, 1968).

Leptospirosis is usually diagnosed from blood serology, despite major difficulties with interpreting the titres. As noted earlier, titres rise rapidly after infection. They tend to fall rapidly soon after abortion but may remain appreciable for years. Titres can drop from 1: 1600 among aborting cows to 1: 400, a titre that may also indicate a recent infection, in three weeks (Deas, 1981). Antibodies may even disappear. A positive titre in the blood or foetal fluid of an aborted foetus is, however, confirmatory.

The bacteria can be cultured but they are usually difficult to isolate from the foetus or membranes, because autolysis of the foetus between infection and abortion quickly results in the death of the bacteria. The bacteria are most readily isolated from the aqueous humour of the eye but can also be isolated from urine. The sample should be inoculated in a transport medium of 1% serum albumin and 5% fluorocil. This can keep Leptospirae alive for 4 days while inhibiting the growth of other bacteria. The presence of the disease is confirmed if the bacteria are seen under dark-ground microscopy or from the post-mortem histopathology of kidney tissue of culled animals. For more detail on the diagnosis and control of leptospirosis, consult Ellis and Little (1986).

Treatment and control

Leptospirosis can be self-limiting. Therefore, all newly-purchased animals should be kept in quarantine and tested for the disease. Hygiene measures outlined earlier for brucellosis should be applied in case of an abortion. Rodents on the farm should be controlled and contamination of drinking places should be avoided by isolating infected animals (Carroll, 1972).

Treatment with streptomycin readily eliminates kidney infection, protecting the herd and people handling the animals. Each aborting cow should therefore be treated with streptomycin at 25 mg/kg bodyweight. Cows usually abort once and may not have to be culled. However, cows that recover can be re-infected.

Carroll (1973) reported an effective vaccine against L. pomona. However, this vaccine does not protect against other serotypes. He recommended annual vaccination of animals in areas where the disease is prevalent.

5.3.1.5 Salmonellosis

Salmonellosis is an important cause of abortion in cattle. It is also a zoonosis. Salmonella dublin and S. typhimurium are the most common causes of Salmonellosis in dairy cattle.

Infected animals excrete the organisms in their faeces, contaminating pastures, water supplies and housing. From these, the bacteria infect healthy animals. Typical symptoms of Salmonellosis include septicaemia, pyrexia and dysentery. Pneumonia may also occur. The bacteria are attracted to the uterus and together with severe enteritis, caused by endotoxins, and painful arthritis, cause abortion (Vandeplassche, 1982). The primary cause of abortion is the release of prostaglandin (PGF2 a) induced by salmonella endotoxin. Following abortion, the uterus may become severely inflamed, resulting in the death of the cow. Cows that recover may continue to excrete the bacteria for years.

Aborted foetuses show no striking features but membranes, retained in about 70% of the cases, are oedematous and yellow, with pus-like exudates. A tentative diagnosis based on these signs can be confirmed by isolating the bacteria from the stomach (abomasum) contents, liver or joints of the foetus, from the placenta or from the dam's faeces.

Salmonellae can be passed to humans. Aborted material should therefore be handled with extreme care. It is difficult to cure carrier animals, and the best control measure is therefore to cull all animals that react positively to tests for salmonella. All animals thought to be infected should be isolated subject to confirmation by isolating the bacteria. This approach is likely to result in better control of the disease than vaccination.

5.3.1.6 Non-specific bacterial infections

Many species of bacteria inhabit the vagina, uterus, and cervix of cows. Some are symbionts that become pathogenic when the animal is stressed; others are immediately pathogenic.

Namboothripad and Raja (1976), Eduvie et al (1984) and El-Azab et al (1988) isolated Staphylococcus aureus, Escherichia coli, Pseudomonas pyocyanea, Corynebacterium pyogenes, Proteus mirabilis, Streptococcus spp., Pasteurella multocida, Proteus vulgaris, Klebsiella spp. and several anaerobic microorganisms from the uteri of cows with a history of repeat breeding, retained placenta and metritis, as well as from the uteri of normal suckling cows. Mycobacterium tuberculosis was isolated by Mohanty et al (1980) from a Haryana heifer that was a chronic repeat breeder.

Listeria monocytogenes may also cause abortion in cattle. When the organism infects a pregnant cow, it invades the foetal nervous system and forms necrotic foci on the liver, lungs and spleen (Watson, 1979), killing the foetus. Vandeplassche (1982) indicated that, although the organisms are easily eliminated from the uterus, they may persist in the mammary system. Antibodies to Listeria are short-lived, and immunity is thus only temporary and cows can be re-infected. Treatment is often futile, even with antibiotics.

5.3.2 Viral infections

Several viral diseases, including infectious bovine rhinotracheitis (IBR), bovine virus diarrhoea/mucosal disease (BVD/MD), pare-influenza-3, G-up, infectious (contagious) bovine epididymitis and vaginitis complex (Epivag), transmissible fibropapilloma and epizootic bovine abortion have been associated with cattle infertility (Florent, 1963; Gledhill, 1968; McKercher, 1969). The major infections are described below.

5.3.2.1 Infectious bovine rhinotracheitis

Infectious bovine rhinotracheitis (IBR) is caused by a herpes virus. Its incidence in Africa is not widely reported but a recent field study by ILCA on two populations of indigenous Ethiopian zebu cattle indicated a prevalence of over 50% (Tekelye Bekele et al, 1989b). IBR can affect the respiratory, reproductive, nervous and digestive systems of cattle. The disease can be transmitted sexually or by droplet inhalation; in its venereal form it has been associated with infertility.

Cows and heifers served by an infected bull develop a pustular vulvo-vaginitis 2 to 3 days later. This may clear up after 2 weeks. Some develop superficial ulcers on the mucosa of the vestibulum and may discharge yellowish pus. Infection rarely extends directly to the cervix or uterus, and therefore pregnancy is rarely terminated. However, if cows are artificially inseminated with semen from an infected bull, the virus is deposited directly into the uterus and induces endometritis. Infection of the uterus disrupts the cow's oestrous cycles and reduces its fertility. The virus may also invade the uterus systemically in cows suffering the respiratory form of the disease.

After invading the uterus the virus may remain dormant for several months. Abortion occurs after 4 to 7 months. The foetus dies soon after being invaded by the virus. The dead foetus may be retained for several days and appear mummified when finally expelled. Haemorrhagic fluid and oedema may be seen in the foetal pleural and peritoneal cavities, with focal necrosis, particularly of the liver.

The above signs indicate IBR. The presence of the disease can be confirmed by isolating the virus from the foetal brain, liver, spleen or lung tissues, placentomes or swabs from the nose, eyes, penis or prepuce. The virus grows best in bovine foetal kidney cell cultures. It can be identified by serum neutralization or immunofluorescence inhibition tests.

The results of the neutralization test may be difficult to interpret. Specific antibodies appear 8 to 10 days after infection and persist for 10 to 20 days (Polydorou, 1984). In general a titre of 1: 32 in a sample taken 10 days after the cow aborted indicates a recent infection. Standard conditions should be followed and maintained while performing the neutralization test because serum dilution, time and temperature of heating the serum, and the time at which the neutralising effect is read affect the sensitivity and reproducibility of the test.

Antibody titres decline after about a month and the antibodies may even disappear. However, even animals that show no serological reaction may remain latently infected. They respond to some stress factor by forming antibodies and shading the virus (Polydorou, 1984). Therefore, a single negative serological test should not be taken as an indication that the animal is not infected.

Control measures against IBR vary. In Switzerland and Denmark all cattle are tested for IBR and those reacting positively to the test are slaughtered. France monitors the disease in bulls because it can be spread in semen. In the Federal Republic of Germany, AI bulls must be vaccinated. None of these systems is used in the tropics.

Carroll (1973) noted a modified live vaccine against IBR. This provided good protection against abortion when given to cows that were not pregnant, but caused abortion in some pregnant cows. Todd et al (1971) reported that pregnant cows could be safely vaccinated intra-nasally.

5.3.2.2 Bovine virus diarrhea

Bovine virus diarrhoea/mucosal disease (BVD/MD) is widespread. It is caused by a Toga-virus. Infection may be acute, mild or chronic. When the virus infects a pregnant cow it may also infect the foetus and kill it. Calves born alive may be stunted, with cerebellar hypoplasia, brain cavitation and mucosal ulceration. These signs aid diagnosis. Confirmation is by the demonstration of antibodies in foetal blood prior to ingestion of colostrum. A double sample with dam's blood is very helpful. A herd test will indicate if BVD/MD was prevalent at the time of abortion.

5.3.2.3 Infectious (contagious) bovine epididymitis and vaginitis complex

Infectious bovine epididymitis and vaginitis complex (Epivag) appears to be confined to East and southern Africa. It was first described in Kenya and subsequently in South Africa (Arthur, 1964). Epivag is a venereal disease. In cows the main symptom of Epivag is muco-purulent discharges from the vagina Epivag can cause permanent lesions on the Fallopian tubes. In the bull, it causes the epididymis to swell, sometimes to the size of a golf ball. The disease can be controlled by slaughtering infected bulls and by using artificial insemination.

5.3.3 Mycoplasmas

Mycoplasmas are infective agents distinct from both bacteria and viruses. Several species of Mycoplasma cause disease in cattle. They have been associated with infertility, but their exact aetiological role is difficult to ascertain because they are present in the tracts of healthy animals.

In a study of cattle in South Africa, Mycoplasma bovigenitalium was found in 43% of males, 47% of females, 25% of foetuses and 11% of placentas (Trichard and Jacobsz, 1985). Mycoplasma ergini, M. alkalescens, M. laidawii, M. bovis, M. bovirhinis, M. verecurdum and M. conjuctivae were also isolated.

Mycoplasmas can be transmitted by discharges from the respiratory and reproductive tracts, and by milk, of infected animals. Infected cattle develop antibodies, but these do not give complete protection.

Symptoms associated with mycoplasmoses can also be observed with other conditions. Diagnosis can only be confirmed by isolating the organisms from nasal or reproductive-tract mucus and discharges, milk, arthral fluids, foetal tissues or the placenta. Consult Trichard and Jacobsz (1985) for procedural details of culture and serology.

The best way to control mycoplasmosis is to cull infected animals.

5.3.4 Endometritis, metritis and pyometra, and the use of prostaglandins in postpartum uterine pathology

Some of the systemic and non-specific infections discussed above can cause endometritis, metritis and pyometra. These pathological conditions are discussed below.

There is little information on the impact of metritis, endometritis or pyometra on the fertility of zebu cattle. Among Bos taurus cattle, Tennant and Peddicord (1968) found that endometritis, as indicated by pus in the vagina, significantly reduces fertility. Cows with endometritis required significantly (P<0.001) more services per conception (2.0 vs 1.6), had lower conception to first service rate (49 vs 62%, P<0.001) and longer calving interval (394 vs 383 days, P<0.001), and more animals were culled for infertility (13.6 vs 6.2%).

Infections of the reproductive tract are usually contracted at parturition. Non-specific infections of the uterus are more common where the placenta is retained, in cows that need assistance with calving and in cows with milk fever. Metritis is often also associated with uterine atony or inertia. Acute metritis causes fever and depression within a week of infection, and is commonly followed by chronic metritis, with persistent purulent vaginal discharge. Specific venereal infections, such as trichomoniasis, campylobacteriosis and brucellosis, may also lead to metritis.

Pyometra is the accumulation of pus in the uterus. It is a common cause of anoestrus and cows with pyometra should be treated promptly. Postpartum metritis, endometritis and pyometra may be common where cows and heifers are confined at delivery time in a building or area in which others have recently calved.

The uterus can resist or eliminate bacteria infection. However, this ability is related to ovarian activity (Paisley et al, 1986). The uterus is highly resistant to infection during the oestrogenic phase but very susceptible during the period of progesterone dominance, because (1) pH in the uterus is low, allowing greater bacterial growth, (2) the epithelium is less permeable to bacteria and therefore the leucocytic system is stimulated at a later stage, (3) the appearance of leucocytes in the lumen is delayed, (4) the activity of leucocytes is decreased, and (5) uterine secretions have no detoxicating effect (Paisley et al, 1986). As a result, some cases of metritis resolve spontaneously when the animal's oestrous cycles resume, while others remain chronic.

Cows with chronic metritis are anoestrous and may have a retained (persistent) corpus luteum. Where a corpus luteum is present, initial treatment should aim at removing it. This is best achieved by an intramuscular injection of prostaglandin. If there is no corpus luteum, endometritis can be treated by infusing antibiotic or sulphonamides into the uterus. Application should be repeated every 2 days for a week. Alternatively, about 100 ml of 2% iodine can be infused into the uterus. The iodine solution is an irritant and stimulates new endometrial growth. Where the oviduct, deeper layers of the uterus or the cervix or vagina is infected, antibiotic should be given intra-muscularly.

Prostaglandin F2 a (PGF2 a) reduces inhibition by progesterone of the uterine defence mechanism. Oestrogen secreted during the subsequent development of a follicle promotes uterine defence. PGF2 a may also stimulate myometrial contractions, helping to empty the uterus of lochia and pus. It may encourage phagocytosis. Jackson (1977) found that a single injection of PGF2 a cured pyometra in 90% of cases. The remaining 10% of cows were cured by a second injection. Prostaglandin treatment may thus be sufficient to clear pyometra and additional antibiotic therapy may be of little advantage (Fazeli et al, 1980).

Several other postpartum conditions can reduce fertility. Cervicitis and vaginitis often follow a delayed or complicated delivery. Metritis may cause abscesses in the uterus; if it spreads to the Fallopian tubes it may lead to salpingitis. Scars in the uterus and adhesions between parts of the reproductive tract can result in infertility or sterility. Routine examination of cows 1 or 2 months after delivery can diagnose such conditions early.

Irrespective of the condition, treatment should also aim at restoring the animal's normal hormonal status. Thus a persistent corpus luteum must be enucleated or lysed. Inactive ovaries should be stimulated using small doses of oestradiol benzoate (2-5 mg i.m.) or diethyl stilboesterol (20 mg i.m. or orally). Cows should be given a period of sexual rest of 2-3 cycles after treatment.

5.3.5 Retained afterbirth

Two to 30% of cows retain their foetal membranes for 12 to 24 hours after a normal delivery. The afterbirth, or foetal membranes, is retained if the cotyledonary villi fail to detach from the caruncular crypts. Membranes retained for more than 2 or 3 days decompose in the uterus, leading to metritis.

The incidence of retained afterbirth is often high in Brucella-infected herds, following a difficult delivery and in cows suffering certain nutritional and mineral (especially selenium) deficiencies. Grunert (1984) categorised the basic causes of afterbirth retention as: immature placentomes, oedema of the chorionic villi, necrosis between chorionic villi and the walls of the crypts, advanced involution of the villi, placentome hyperhaemia, placentitis and cotyledonitis, and uterine inertia.

Cows with retained afterbirth have poor appetite and reduced milk and meat yields. Their fertility is reduced, especially if metritis develops.

Treatment of the cow with retained afterbirth should be aimed at expelling the afterbirth and preventing infection of the uterus. In treating a cow with retained afterbirth, it should be remembered that removing the afterbirth by hand may be harmful to the cow; it may cause haemorrhage, haematomas and vascular thrombi in the uteri, reducing subsequent fertility. The operator may also fail to remove all the afterbirth. There is also the risk of contracting brucellosis from handling retained afterbirths. Banerjee (1963) found, for example, that conception to first service among European Bos taurus cattle in which the retained afterbirth was manually removed was only 39%, compared with 50% among cows in which no treatment or removal of the afterbirth was undertaken. Manual removal with an intra-uterine infusion of oxytetracycline also resulted in 39% conception to first service. In contrast, intra-uterine treatment with oxytetracycline alone without removal of the afterbirth resulted in the highest conception rate (70%). More recent work by Bolinder et al (1988), showed that manual removal delayed establishment of the first functional corpus luteum by 20 days in Holstein cows induced into parturition.

Proper animal husbandry can reduce the incidence of afterbirth retention. Animals should be sexually rested for at least 2 months after calving, fed a balanced ration, adequately exercised where they are continuously raised indoors and immunised against prevalent infectious diseases that cause abortion. Animals should not be unduly stressed and proper sanitation and management must be exercised at delivery; selenium should be added to feed where it is deficient (Youngquist and Bierschwal, 1985).

5.4 Summary

Among the common forms of functional infertility in cows are faulty oestrus manifestation including silent heat, inactive ovaries with anoestrus, cystic ovaries, abnormal oestrous cycle periodicity, and repeat breeding due to delay or failure of ovulation and fertilization or early embryonic death. These forms of infertility tend to affect individual animals, but they are becoming more important as attention is paid to the environmental and health constraints.

Several systemic, genital and non-specific infections of the reproductive tract reduce the fertility of zebu cattle. Some are also important zoonoses. Their exact frequency in many areas is not precisely known and warrants further study.

The best way to control many of these diseases is to prevent contact between herds. If this is not practicable, herd owners should buy only virgin heifers as replacement stock. All newly introduced stock should be quarantined for 3 to 4 weeks before joining the herd.

Farmers should not buy bulls that have been used for breeding in other herds unless they are proved to be completely free of important diseases. Semen for artificial insemination should be obtained from reputable centres.

All replacement heifers should be vaccinated with Brucella Strain 19 vaccine when 3 to 6 months old. Older animals should be given Strain 45/20. Once the incidence of brucellosis has been reduced, the herd should be regularly tested and infected animals culled.

The modified live virus vaccine for infectious bovine rhinotracheitis confers good immunity, and all heifers should be vaccinated.

Cattle can be vaccinated against both campylobacteriosis and leptospirosis annually. The vaccines are, however, expensive and may not be readily available, and even a vaccinated bull can act as a passive vector) after serving an infected cow.

Infections of the uterus can be largely avoided by having cows served and calved under hygienic conditions. Cows should be allowed plenty of room during calving, and the site should be clean. Bedding should be changed after each calving. When conducting obstetrical manipulations, use only disinfected instruments and disinfect both the operator and animal before and after any manipulations. If a birth is difficult, or otherwise abnormal, intra-uterine application of a broad-spectrum antibiotic will help prevent infection.

All infertile animals should be examined to determine the exact cause of their infertility. If a cow aborts, the aborted material should, if possible, be sent to a diagnostic laboratory to ascertain the cause.

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