Reproduction is directly affected by various management related factors. Manipulation of these factors can cause changes in reproductive performance. The control and manipulation of the sheep reproduction has been the objective of scientists around the world for many years and more recently the goat is also being studied, because some reproductive characteristics which appeared similar with sheep, after more detailed studies, were found to be quite different.
High levels of reproductive performance can only be achieved under optimum management conditions (including nutrition). This is one factor that determines the dramatic differences in reproductive efficiency between the developed and the developing countries (where the nutrition and general management of the flocks are not quite good). In developed countries of the western hemisphere most of the sheep or goat populations are maintained in small or medium size flocks with more or less intensive systems of production whereas in developing countries (like Peru for instance) the sheep population is exploited in extremely large flocks (80,000 to 200,000 ewes per flock) in extensive systems or in very small flocks (20 to 50 ewes) in the hands of Indian communities with very poor levels of education. The structure of goat production is also quite different in developing countries where the goat flocks are in the hands of nomads and poor goat keepers.
The structural aspects of land (pasture or natural resources) distribution are important factors that determine the possibility of using different systems of production and technology in the small ruminant production. This coupled with the educational level of the farmers and the potential of the available resources (cultivated or natural pastures, rain distribution, water avaiability, ecological environment, etc.) finally decides which practices or technologies can be applied economically to improve the productivity. In addition the “cost of the technology” is an additional factor that has to be considered and can explain partially why in developing countries the use of modern reproductive techniques that are in practice in developed countries (e.g. controlled breeding) are not applied in developing countries on a commercial scale. The big differences in the economic and financial situation between the north and the south are reflected also in the application of technology. Most of the recent developments in reproductive techniques have to use some hormones or imported products that are expensive for producers in the developing countries.
Apartado 456, Lima, Peru
The preceding considerations explain why existing technology in small ruminant reproduction is not being used in developing countries. On the other hand, the objectives in terms of reproductive aspects can be quite different depending on the type of resources that the small ruminant population is using (e.g. twin lambs are difficult to maintain in natural pastures in the Peruvian highlands).
MAIN AREAS OF DEVELOPMENT IN REPRODUCTIVE TECHNIQUES
Sheep and goats because of their gestation period of about five months and the possibility to produce more than one offspring per pregnancy are species whose production methods can still be greatly intensified. In order to maximize the production potential of a small ruminant flock (sheep or goats) it is essential to increase the reproductive rate. There are a group of factors which limit reproductive efficiency namely those which influence the fertility, the fecundity, the lamb survival and the interlambing period. The development of reproductive techniques are directed to solve or minimize the effects of these limiting factors as well as to make possible the application of more intensive systems of production and to facilitate the genetic improvement of the productive characteristics of the flock.
Reproductive techniques in sheep
The main areas of research activity on advanced techniques in sheep reproduction can be summarized as follows:
Manipulation of the breeding cycle:
Out of season breeding - more frequent lambings
Breeding at younger ages
Control of lambing - induction of parturition
Manipulation of the breeding cycle
Attempts to control oestrus and ovulation in sheep during the breeding season and anoestrus are based on simulating the activity of the corpus luteum, producing progesterone in quantity for about 2 weeks and in shutting off production sharply at the end of the oestrus cycle. Progestagen administration was made commercially feasible by the work of Robinson (1964) using the progestagen impregnated sponge inserted intravaginally. The technique of vaginal sponges for the control of the oestrus cycle in the ewe is now well developed in France and this system is spreading in Spain, Italy, Holland, Germany, Isreal and in some East European countries.
Synchronization of oestrus during the breeding season: One application of the progestagen technique is the synchronization of the ewe's oestrus during the breeding season, so that all ewes will show oestrus simultaneously during a 3-day period. Different procedures are in use for this purpose:
Vaginal progestagen pessaries
Only compounds with characteristics identical to progesterone, especially in having short duration of activity, are suitable (Robinson, 1976). These compounds, according to studies in Australia (Robinson et al., 1968), Ireland (Gordon,1971) and France (Colas, 1975) are flurogesterone acetate (FGA) and medroxyprogesterone acetate (MAP). When FGA (30 mg) and MAP (60 mg) have been compared in ewes by artificial insemination, a small but significant advantage in favour of FGA was found (Smith et al., 1981). As well as the question of the particular progestagens which are regarded as acceptable for intravaginal applications there are two other important considerations; dose level of compound and method of impregnation employed in the preparation of sponges (Gordon, 1983). Robinson (1968) mentioned that a progestagen dose which will inhibit ovulation in the cyclic ewe is lower than that required for full fertility. The rate of absorption of FGA from intravaginal sponges can be significantly affected by the impregnation procedure and by the initial dose of compound (Robinson et al., 1968). Absorption rate significantly affected the percentage of ewes in oestrus and the number of sheep lambing to service at the controlled heats. Gordon (1971) reported that a significantly higher mating response and lambing outcome resulted from thorough dispersion of a 30 mg dose of FGA in the sponge matrix. The dose of FGA which can be regarded as optimal, lies in the range of 20–40 mg. With MAP, the 60 mg dose appears to be the standard currently (Gordon, 1983). The procedure currently used for oestrus synchronization during the breeding season is to insert the vaginal progestagen pessaries (MAP or FGA) in the vagina for 14 days, creating an artificial cycle for all ewes. When the pessary is removed ewes will show oestrus 2 to 4 days later (Bindon, 1982).
An alternative approach to the intravaginal sponge in sheep is the subcutaneous implant containing the natural hormone, progesterone. Leman et al., (1970) used implants impregnated with 375 mg of progesterone, others have reported the same technique (Doane, 1971; Zenoulis et al., 1972; Gordon, 1975). The implant is inserted under the skin in the brisket region and removed 14 days later. Ewes show oestrus 2 to 3 days after implant removal. According to Gordon (1983) using the progesterone implants in Ireland it has not been possible to match the speed and simplicity of the intra-vaginal sponge technique.
The prostaglandin F2α works by inhibiting the production of progesterone from the ewe's ovary. During the normal oestrus cycle in the ewe prostaglandin F2α is synthesized and released from the uterus, causing the regression of the corpus luteum (McCracken et al., 1970; Goding, 1974). In comparison with the oestrus response after progestagen treatment in ewes, the incidence of oestrus that follows the prostaglandin method may be much lower (Gordon, 1983); also the fertility rate is depressed (Bindon, 1982). If the natural prostaglandin F2α agent is employed, the accepted luteolytic dose of 15 mg is about 60% of that required in the bovine; using the cloprostenol analogue, 100 μg has been employed as a luteolytic dose, which is only 20% that employed in the cow (Gordon, 1983). In comparison with the progestagen or progesterone treatment the prostaglandin (PG) treatment is more expensive. In order to use PG the ewe must be in the 5th-13th day of her cycle, so that to synchronize, all ewes in the flock, 2 injections are given 9 days apart. Ewes show oestrus on 2–3 days after the second injection. Table 1 shows a comparison made by Bindon (1982) between the synchronization methods.
Synchronization methods can be useful in A.I. programs or in hand service in some smaller studs wanting to reduce spread of lambing to allow maximum supervision. In Peru we used the intravaginal sponges with MAP in 40 ewes syncrhonized during the breeding season this March 1985 to perform embryo transfer using frozem embryos from Montana (USA) to introduce Finn sheep in Peru. The use of synchronization methods in developing countries can have justification in genetic improvement programs in selected studs from which the genetic material then can be distributed in other flocks.
Some disadvantages of the use of synchronization of oestrus during the breeding season are the necessity of a higher ram:ewe ratio than in natural mating for maximum fertility. Also lambing figures will not be improved and may be slightly reduced.
Out of season breeding: Progesterone implants and progestagen intravaginal sponges also can be used for out of season oestrus induction in sheep. In most out of season applications it is also considered essential to augment the supply of exogenous gonadotrophin by administering a follicle-stimulating agent on completion of the progestagen treatment. The cheapest, most readily available and consistently effective gonadotrophin for this purpose is PMSG. So ewes may be induced to breed outside their normal sexual season by the combined use of a 12 day progestagen phase to simulate the oestrus cycle and an injection of a gonadotrophic hormone, usually PMSG, to cause ovulation. With this method the ewe shows oestrus 48–60 hr after PMSG (400–700 i.u.) which is injected at the time of sponge or implant removal. Fertility should be 60 to 70% (Bindon, 1982; Vivanco et al., 1985). Table 2 shows a summary of results in different locations in the world. This procedure is now used on 1 million ewes per year in France and about 20,000 per year in the U.K. and Ireland (Bindon, 1982). The objective in almost all cases is to advance breeding season with a view to producing early lambs to catch a market premium. This method also could be used to create 2 lambings per year (Cognie et al.,1980).
Unfortunately, in developing countries, the lamb market is not organized and the commercialization and prices fluctuate at ramdom, sometimes the government fixes or regulates the prices so the lambs born out of season have no premium. In addition lambs born out of season, if there are no cultivated pastures available, cannot be grown successfully. So the use of out of season breeding to advance the lambing season or to produce 2 lambings per year is only feasible in flocks with very good management and with good feed supply; this type of farm is very scarce in developing countries This implies the necessity to combine reproduction improvement programs with pasture improvement and technical assistance.
Table 3 shows the results from one experiment in Peru using progesterone implants and FGA sponges for out of season breeding in ewes in the Peruvian highlands under natural pasture conditions at 3,800 m above sea level. Fertility was less than in the breeding season but fecundity was higher because of the effect of PMSG.
Recent research shows that the “Ram Effect” (the ability of the odour of the ram to induce oestrus) in anoestrus ewes may be used to replace injection of PMSG; ewes must have been isolated from rams for at least 4 weeks. The ram is introduced on the day the vaginal sponge is removed.
The manipulation of the breeding cycle in ewes can be done also by artificial day length control (Gordon, 1983). It can be a matter of providing a gradual decrease or increase in artificial day length, similar to what occurs under natural day length conditions or it may be done by subjecting the ewes to an abrupt decrease on one day and thereafter maintaining them at that day length until a response is shown (Fraser and Laing, 1969). One partial disadvantage in using day length control is the fact that individual ewes show oestrus after varying intervals; several weeks may elapse between the time and the first and the last sheep in the flock comes on heat. Obviously this system requires electrification of the rural areas.
Breeding at younger ages
The age at first parturition is critically dependent on the growth rate of the ewe lamb, so if the feed availability is short or the genetic characteristic of the sheep is not for fast growth, the age at the first parturition will be delayed. But in some circumstances the intensification of the production systems allows a reduction of the interval from birth to first mating and this can have obvious benefits: reducing maintenance costs, shortening the generation interval, increasing the genetic gain and increasing lifetime production. In Peru for example, young ewes maintained extensively in natural highland pastures are currently mated at 18 months of age, whereas in other parts of the world most sheep farmers breed ewes for the first time at the yearling stage. For the Peruvian farmers that are introducing cultivated pastures, it is of interest to start breeding the ewe at one year of age because at that age they reach the same body weight as the 18 months old ewes in natural pastures. For ewes that are one year in November (anoestrus period or very poor oestrus activity) some technique of oestrus induction has to be apllied. In other locations of the world the objective is to mate at 7–8 months of age to have first lambing at one year of age.
In France where controlled breeding is now used on some scale in ewelambs, it is recommended that ewe lambs should be 60–65% of their mature weight and older than 7 months before being induced to cycle using the FGAPMSG technique (Thimonier et al., 1968).
In farming situations where the full genetic potential of the particular breed is being achieved and a further improvement in litter-size is considered desirable, then the introduction of a more prolific breed, selection of ewes within a breed or the artificial control of litter-size are among several of the options available (Gordon, 1983).
In Peru, the sheep breeds (Corriedale, Junin and Criollo) have very low ovulation rates and the incidence of twins under natural pasture conditions is extremely low. Under cultivated pastures the Junin breed increases slightly in twinning percentage (about 2% of twinning); so in cultivated pastures it is necessary to increase the fecundity of ewes in order to have more profit per hectare. The genetic approach requires more time to introduce and or select the characteristic. Physiological methods, like the use of exogenous gonadotrophin or the immunization against sexual steroids, are interesting alternatives that have the advantage that they can be applied under the decision and control of the farmer according to the feed availability.
Use of PMSG to increase the fecundity
Lambing figures may be increased by treating ewes with PMSG applied on day 14 of the oestrus cycle. This is somewhat similar to the out of season breeding technique. An injection of approximately 400 i.u. of PMSG should increase the number of lambs weaned by about 20% (Bindon, 1982). Ewes must be synchronized so that day 14 can be easily identified. The schedule recommended is: insert MAP sponges day 1, remove MAP sponges day 14, inject PMSG day 30, days 33–36 expect ewes on heat with normal fertility. A disadvantage of the use of PMSG is the long half life of this hormone so the response of the ewes is variable; in our experiment we found ewes with five corpora lutea after 700 i.u. of PMSG treatment and some triplets at lambing.
Immunization against steroid hormones to increase lambing percentages
Immunization of the ewes against their own oestrogenic steroid hormones is a new method of increasing lambing percentages of sheep due to the increase in the ovulation rate. The procedure was developed by the CSIRO Division of Animal Production (Cox et al., 1976; Scaramuzzi et al., 1977). This technique offers the potential of an immediate gain in ovulation rate and lambing percentages, the flexibility of a decision each season and the possibility of a simple treatment (Cox, 1983). Active immunization is considered likely to be more practical than a passive system. Ewes are vaccinated against their own oestrogneic steroid hormones and this has the effect of upsetting the system which regulates the number of eggs shed.
From the results obtained by the CSIRO team up to mid-1982, a basic protocol was defined giving optimal results with an androstenedione -7-HSA immunization. In this, 1.2 mg androstenedione -7-HSA in 5% DEAE-Dextran/0.9% sodium chloride solution, is administered in 2 ml at a single site subcutaneously in the upper third of the neck. Spacing between first and second treatment is 3–5 weeks. Synchronization of oestrus is not required. Rams are joined 2–3 weeks after the second injection or after the booster injection in subsequent years. If rams are joined earlier than 2 weeks, poor results are likely (Cox, 1983). Table 6 shows some results from New Zealand quoted by Bindon (1982). The immunization method is now commercially available in Australia, New Zealand and U.K. Table 7 shows the results obtained by the commercial applications.
The application of immunization increases lambing percentage by between 20 to 30% in breeds likeCorriedales that have currently a low twinning percentage.
Obviously the increase in fecundity requires good management and food availability, so the application of these methods are limited to farms in which this requirement can be achieved. In developing countries farming is generally carried out in harsh environments. This condition determines that the reproductive rates are poor compared with the standards of the temperate countries. Efforts are in progress to improve the pastures and farming conditions; for instance in Peru some large co-operatives are irrigating lands in the highlands to cultivate ryegrass and clover. On cultivated pastures the ewes have to achieve a higher reproductive performance in order to utilize the better resources. In those cases the use of techniques to increase lambing percentage can be justified.
Control of lambing - induction of parturition
The main objective for the use of techniques for control of lambing is to reduce labour, to supervise more closely the lambing of stud ewes, or to induce premature lambing in pelt producing sheep (Karakul). These techniques are used in highly sophisticated intensive sheep systems. French research has led to a successful technique for reducing the spread of lambing. It is based on the injection of a hormone (Dexamethasone) which mimics the action of the signal normally produced by the foetus to initiate parturition. Ewes are injected on the evening of day 144; it is thus essential to know the date of conception. Lambings will normally be confined to a 48 hr period and about 75% will occur during daylight hours (Bindon, 1982).
Part of the reason for interest in compact lambing is in being able to reduce lamb mortality by the application of well-proven management techniques for ensuring survival of the lambs (Gordon, 1983). In the Peruvian highlands, lamb mortality reaches about 25% due to the negative effects of climatic factors (frost, limited food availability, etc.). Closer observation of the flocks during lambing can help, especially in the stud flocks, to reduce the lamb mortality.
The interest in sheep farming of early pregnancy detection is based on the necessity to select the pregnant ewes to give them better feeding and attention and culling barren ewes. In some farms in which twinning is expected there is an additional interest to determine whether the pregnant sheep is carrying multiple foetuses so that special management can be applied before and at the time of lambing to eliminate lamb mortality.
Several methods have been developed: radiographic techniques, progesterone and oestrogen tests, ovine placental lactogen, immunological tests, vaginal biopsy, laparotomy, ultrasonic techniques, rectal-abdominal palpation, manual examinations (Gordon, 1983). From these very few can be used practically and economically at farm level; perhaps the most practical one for simple early diagnosis is the detection of the fluid filled uterus by A-mode sound. The ewe is usually dealt with in the standing position, the transducer is smeared with oil and placed on the bare skin of the belly about 50 mm in front of the udder on the ewe's right side. When the narrow beam of ultrasound meets tissue which has a different acoustic value (like the fluid filled, pregnant uterus), it is reflected at the boundary of the object; the echoes are received by the transducer and converted into signals which are amplified and displayed on a cathode ray screen or in some other visual form (Gordon, 1983). In Peru we are applying this method since 1980, the ultrasound was introduced by the Small Ruminants Collaborative Research Program US-AID (CRSP-US-AID). The diagnosis is done between 40 to 50 days with 96% of accuracy.
To diagnose multiple births during pregnancy, Bindon (1982) refers to techniques potentially available such as the real time ultrasound scanning and the plasma-glucose measurement (ewes carrying twins or large singles have significantly lower blood glucose from about day 90 of gestation).
Artificial insemination in sheep
Artificial insemination (A.I.) is a reproductive method of great influence in the improvement of productivity. The advantage of A.I. has to be coupled, however, with an appropriate reproductive rate. That means that the A.I. must not have a detrimental effect on conception and lambing rates. The effort of the research centres has been focused on increasing the viability of the semen doses, especially testing different diluents. The most distinctive characteristics of A.I. in sheep are probably:
the necessity to have large quantities of sperm cells in the insemination doses in comparison with the concentration of spermatozoa in bovine insemination (100 to 500 million sperm in sheep vs. 10 to 30 million sperm per A.I. dose in bovine).
The relatively short effective life of the refrigerated diluted semen (24 hours vs. 3 days in bovine).
The anatomical obstacle of the ovine cervix, not permitting the access of the insemination pipette deeply in the cervix (Bunch and Ellsworth, 1981).
The extensive practice of insemination with raw semen.
The limited use of frozen semen due to the low fertility rates obtained.
The non-existence of commercial A.I. organisations for the sheep industry; most of the inseminations are done with semen collected on the farm.
These characteristics are in some way determining that A.I. is not in sheep the main reproductive method and genetic improvement tool whereas in bovine the importance of A.I. is enormous. The use of A.I. in sheep in Western Europe and United States of America is very limited; France is one of the countries in Western Europe in which A.I. is developed. In the Soviet Union and some Eastern European countries A.I. is more widely used. In Peru, the total number of ewes inseminated per year is about 300,000 compared to 40,000 cows inseminated per year, so in terms of total numbers we are inseminating more ewes than cows. The organization of the sheep industry in each country determines the relative importance of the use of the A.I. The genetic improvement systems, selection pressure and availability of rams are some of the determining factors.
In Peru, the sheep population consists mainly of “Criollo” animals introduced by the Spanish 400 years ago; those animals became naturalized to the harsh environment of the highlands, but sacrificing their productive characteristics because of the lack of genetic improvement programs. Thirty to fifty years ago the introduction of improved breeds like Corriedale led to crossing with the Criollo sheep. Since that time there have been periodic imports of rams from Australia, New Zealand and other countries. These rams are intensively used through artificial insemination using either raw semen or fresh diluted semen; the fertility rates fluctuate between 60 to 70%.
It is probable that by increasing the viability of refrigerated and frozen semen A.I. in sheep can be greatly improved; because semen is deposited only in the entrance of the cervix then semen with low viability cannot reach the fertilization site with enough capacity to fertilize the ova. Experiments with intra-uterine insemination have demonstrated higher conception rates using frozen semen compared with cervical insemination; this demonstrated that if the sperm cells can avoid passing through the cervical canal they can be much more fertile (Fukui and Roberts, 1976; Maxwell etal.,1983).
In Australia the use of the endoscope for intra-uterine insemination with frozen semen has given very good fertility (Maxwell et al., 1983). The results are shown in Table 8. According to these results, successful A.I. with frozen semen can be done at 60 hours after FGA sponge removal, inseminating 40 × 106 sperms per uterine horn by endoscopy.
In Peru, we have been interested in developing A.I. in sheep with frozen semen; so we started, in 1978, comparing different diluents and freezing methods. In 1980, we inseminated 34 ewes with frozen semen using tris-egg yolk diluent. The semen was stored in ampoules in liquid nitrogen. The insemination was carried out by the cervical method with doses containing 80 million sperms. The lambing rate was 57.9%. The semen was processed at the National Agrarian University in Lima and the inseminations were done in the highlands (Table 7).
Due to the help of the International Atomic Energy Agency in our research activities in Peru, we have the advice of CSIRO Scientists from Australia. This has led to the importation of semen from proven Corriedale rams. The semen was frozen in pellets at the University of Sydney and imported into Peru in October 1984. We inseminated 1,000 ewes (in commercial scale) in November 1984 (out of season breeding), synchronizing the oestrus with FGA vaginal sponges and PMSG (500 i.u.); we inseminated an average of 150 ewes per day using two endoscopes, applying the semen by intra-uterine insemination 54 to 60 hours after sponge removal. Each pellet served for two ewes and each ewe received 40 × 106 spermatozoa in each uterine horn. In February 1985 pregnancy diagnosis by ultrasound showed that 65% of the ewes were pregnant. The expectation of the Peruvian farmers in this trial is high because they could in the future replace the importation of rams by frozen semen from proven rams and have the benefit of the selection work of Australian breeders. Apparently the use of the endoscope is considered to be complicated but with some practice it is relatively easy. For the large Peruvian co-operatives it is justified to invest in one endoscope for A.I. with imported frozen semen. Of course the utilization of A.I. and especially imported frozen semen has to be a decision made having regard to all the factors (genetic, ecological, economic, etc.)
Embryo transfer in sheep
The A.I. must have an important role in the genetic improvement of the sheep population; through A.I. selection, genetic improvement through cross-breeding can be done gradually and economically. In some circumstances, when it is decided to introduce a new breed, or to boost the population of a particular breed, the use of the embryo transfer (ET) can be an interesting alternative. The ET technology requires the superovulation of donors, breeding of the donors, recovery of eggs, evaluation of the embryos, handling and preservation of embryos, synchronization of recipients, transfer of the embryos. Each of these phases has its own characteristics and problems; research activities have been focused to solve the difficulties in each step and to define an economical and practical methodology.
To some extent, the superovulation of sheep can be considered satisfactory either using PMSG (Lawson et al. 1972) or HAP (horse anterior pituitary) (Moore and Shelton, 1964a). The fertilization rates obtained in superovulated ewes are also considered appropriate (Moore, 1974). The technique applied for the recovery of eggs due to the anatomical limitations of the ewe, is a surgical method (laparotomy) that involves flushing the eggs from the reproductive tract (Holstand Braden, 1972; Moore and Shelton, 1962a, b, 1964; Trounson and Moore, 1984a-c; Tervit and Havik, 1976). Using the surgical approach more than 80% recovery has been achieved, but perhaps the necessity to perform surgery is the main limitation in the development of ET as a practical field method. The embryo evaluation of sheep eggs can be done by stereoscopic microscopy with a high degree of precision (Moore, 1970) and the short or long-term storage of embryos has also been developed for sheep (Adams et al., 1961; Lawson et al., 1972; Moore and Bilton, 1976). Most of the ET was performed under experimental conditions, however, some commercial organizations are now in progress.
The laparoscopic embryo transfer is an interesting alternative. Shiewe et al., (1984) describe a very practical method of embryo transfer using the laparoscope, comparing laparotomy vs. laparoscopy. They realised 16.6and 50.0% of pregnancy rate, respectively. The laparoscopic approach is probably one of the most promising aspects in the future development of ET as a practical method in the field. Through the CRSP - US-AID Program, Finn sheep will be introduced to Peru in order to perform some genetic trials to increase reproductive rate. For this purpose, 40 embryos will be transferred to recipient ewes in Peru; the embryos were frozen in Montana State University (USA). The embryo transfer will be done by laparoscopic technique on 17th of April 1985. This is an example of how genetic material can be introduced at lower cost into developing countries.
Reproductive techniques in goats
As was mentioned before, goats differ from sheep in some reproductive characteristics; for instance the length of the oestrus cycle in goats is on average 20 days, in sheep 17 days; the length of oestrus is 34–38 hours in goats, 24–36 hours in sheep. Ovulation occurs in sheep 24 hours after onset of oestrus (Bearden and Fuquay, 1980) whereas in the goat ovulation occurs 34.5 ± 6.6hours after the onset of oestrus (Gonzales Stagnaro, 1984). In addition there are some anatomical differences; the cervix in goats is approximately 3–4 cm in length with 3–6 folds (Simplicio et al, cited by Riera, 1984). In sheep the cervix is 6 cm in length with 5–8 folds (Wond 1958, cited by Riera, 1984). But perhaps the most important anatomical difference is that in goats all the folds of the cervix have a straight alignment whereas in the ewe the second posterior or caudal fold is not aligned with the other folds conferring a tortuous lumen of the cervix (Bunch and Ellsworth, 1981). The anatomy of goats enables deep intra-cervical or intra-uterine insemination through the cervix and may affect approaches for non-surgical recovery and transfer of embryos.
Other differences between sheep and goats were found in the number of placentones, being higher in goats; in the endocrinology of gestation and parturition, the corpus luteum remains active throughout the gestation in the goat; males influence differently the initiation of the oestrus cycle in goats; better responses are found in goats to superovulation than in sheep and also in embryo yields and embryo survival which are higher in does than in ewes (Riera, 1984).
There are some similarities between the species. Sheep and goats are “short day” breeders, can have multiple births, the gestation length is similar as is the postpartum anoestrus.
The seminal characteristics however are different; buck semen has to be handled and processed in a different way (Nelson, 1981; Corteel, 1975). The actual insemination procedures for goats are essentially similar to those in sheep (Salamon, 1976).
Initially, work on reproductive techniques in goats using procedures successful for cattle and sheep were disappointing. French workers started to study goat reproduction more closely contributing greatly to the application of specific reproductive techniques for goats. Today methods of control of the breeding cycle, artificial insemination and embryo transfer in goats are effective.
Control of the breeding cycle in goats
The control of the oestrus cycle can be done in the mating season to synchronize the cyclic does, or for fixed time A.I.(Cortell, 1975; Moore, 1974; Hearnshow et al.,1974).
In the non-breeding season, the induction of oestrus and ovulation in does is also possible (Corteel, 1975).
Control of oestrus during the mating season
During the mating season oestrus can be synchronized by either intra-vaginal progestagen pessaries, progesterone implants or prostaglandin. Does show oestrus 36–48 hours after the removal of pessaries or implants (Moore and Eppleston, 1979). Moore (1980) applied 30 mg FGA in pessaries inserted for around 18 days. A small dose (about 300 i.u.) of PMSG was applied at the time of removal. Corteel (1975) used 45 mg FGA for 18–21 days.
When a single injection of 100 μg of a prostaglandin analogue “Estrumate” (I.C.I.) is used, oestrus occurs one day later and with somewhat less precision than after pessaries (Moore and Eppleston, 1979). In the doe, corpora lutea during the first 4–5 days after oestrus are not sensitive to the luteolytic action of prostaglandin. This problem may be overcome by two injections spaced 10–12 days apart (Moore, 1980).
Control of breeding cycle in the non-breeding season
The goat in most temperate areas of the world is a short-day breeder with peak breeding activity occuring during late summer, autumn and early winter (Moore, 1980). In tropical regions close to the Equator there is some evidence of polyoestric activity throughout the year (Gonzales Stagnaro, 1984) but still more observations are required in these regions. To induce oestrus and ovulation in the anoestrus does progestagen pessaries with PMSG can be used but fertility is dependent upon stage of anoestrus and time of treatment postpartum. In dairy breeds conception rates at induced oestrus are not high until around one month before the start of full breeding activity and during lactation full fertility is not restored until some three months after kidding (Corteel, 1975).
Most recently (Corteel et al., 1984) described two different treatments to induce oestrus and ovulation in the anoestrus dairy goat; a Long Lasting Progestagen Treatment (LLPT) (45 mg of FGA administered by vaginal sponges for 21 days) associated with PMSG (500–700 i.u.) injected intramuscularly 48 hours before sponge removal. The Short Lasting Progestagen Treatment (SLPT) (45 mg of FGA administered by vaginal sponges but for 11 days) associated with two intramuscular injections, one of PMSG (500–700 i.u.) and one of cloprostenol (PGF2 analogue - 200 ug) both given 48 hours before sponge removal. Fertility based on blood plasma progesterone levels was slightly higher after Short Lasting Progestagen Treatment than after Long Lasting Progestagen Treatment (72.5% vs. 68.2% ); kidding percentages were significantly higher, favouring the Short Lasting Progestagen Treatment (62.4% vs. 54.9% ). The results are shown in Table 8; the month of A.I. also had an influence. Based on the results reported by Corteel et al., (1984) we applied the Short Lasting Progestagen Treatment on 90 does (Anglo Nubian) in the Peruvian central coast; all of the does showed oestrus after treatment (average 36 hours), then we inseminated with frozen semen donated by FAO through the CRSP; the semen was from the USA. The insemination was performed 18 hours after onset of oestrus. The fertility was poor (less than 40% ); the experiment is still in progress, The inseminations were carried out in November–December (spring); these results are in concordance with the explanation made by Corteel (1975) describing low fertility rates in dairy goats at induced oestrus in out-of-season breeding, until one month before the start of full breeding activity.
Artificial insemination in goats
The development of intensive dairy goat farming in some European countries, North America and New Zealand has motivated the use of A.I. in order to prove bucks through progeny testing for milk production. This factor coupled with the accessibility of the doe cervix for intra-cervical or intra-uterine insemination have facilitated the use of frozen semen and the development of commercial organizations for A.I. in goats.
Compared with sheep the A.I. in goats is more accepted by the farmers, some are using A.I. as the main reproductive technique in their flocks. Semen can be collected, either by artificial vagina or by electro ejaculation. When the semen is used fresh, it can be diluted with heat-treated cow's milk. Conception rates higher than 60% have been achieved with semen diluted 2:1(milk: semen) and using a volume of 0.1ml (Moore and Eppleston, 1979). Diluents containing egg yolk have given rise to very irregular fertility results; kidding rates after a single insemination ranged from 5% to 85% and the improved fertility results reported were never repeated (Corteel 1973). The very poor fertility results obtained by inseminating goat semen preserved in media containing egg yolk may be attributed to high concentrations of lysolecithins in the environment of the sperm cells (Corteel, 1981). These high concentrations are toxic to spermatozoa (Corteel, 1980). Lysolecithins result from the hydrolysis of egg yolk lecithins to lysolecithins and fatty acids; the hydrolysis being triggered by an enzyme secreted in large quantities by the bulbourethral glands of the male goat (Corteel, 1981). So up to now dilutions using cow's skim milk give fairly steady fertility results when semen is maintained at 6°C. But, as a general rule, when extended semen is stored at temperatures above 0°C sperm cell survival is of short duration (a few days) and sperm fertilizing ability cannot be preserved at a high level for more than a few hours (Dauzier,1966).
Insemination with undiluted fresh semen or with liquid stored semen can be used when bucks and recipients are in the same location. With the liquid stored semen short distance shipping of semen is possible; this can be a good tool for Regional Programs of genetic improvement.
Long term storage of goat semen by freezing has been reported by different workers (Bonfert, 1956; Corteel, 1974, 1975; Fougner, 1974; Nelson, 1981) using various diluents and freezing methods. Spermatozoa frozen together with the seminal plasma did not stand storage for more than 2 months (Corteel, 1975); fertility rates better than 50% were obtained only after removal of most of the seminal plasma from the environment of the sperm cells by washing them through dilution and centrifugation before cooling, freezing and thawing, but when ejaculates of high volume are produced the improvement of sperm cell freezability is not substantial (Corteel, 1981). Although non-breeding season seminal plasma is more detrimental to sperm motility than breeding season seminal plasma (Numes, 1980) it is more readily and efficiently removed by the washing procedure because the volumes of the ejaculates are low (Corteel, 1981).
These difficulties in freezing goat sperm is one limiting factor for the development of the A.I. in goats using frozen semen, but some commercial organization are operating using sophisticated methods for freezing. The fertility results after insemination with deep frozen goat semen are variable and are dependent on the freezing method, time of insemination from onset of oestrus, number of inseminations per heat period, concentration of sperms per dose of insemination and site of semen deposition. There are different recommendations in relation to these aspects. Corteel (1981) reported better fertility and kidding percentage following insemination between 0–12 hours after the detection of oestrus. We obtained a better kidding percentage by inseminating at 24 hours after the onset of oestrus and reinseminating at 30 hours after onset of oestrus (Vivanco et al., 1982) with frozen semen donated by “Caritas-Suiza”. Tables 9 and 10 show the results obtained by Corteel and our results. One advantage of goats in relation to sheep is the possibility to introduce the insemination pipette deeply into the cervix; this allows placement of the semen in the uterus without surgery.
The use of A.I. in developing countries can be a very important tool for genetic improvement programs, introduction of specialized breeds, development of selection programs and progeny testing. It is necessary to continue research in freezing methods to find more simple, less sophisticated methods and with better fertility results.
Embryo transfer in the goat
There are very few reports on embryo transfer in the goat, but the results are encouraging and demonstrate that procedures used for transfer in sheep might be successfully applied to the goat. In brief, embryo transfer involves superovulation of donor females with PMSG or HAP, mating, collection of embryos and their transfer to recipient females. Moore and Eppleston (1979) have demonstrated the value of embryo transfer in the Angora Goat. They obtained 393 Angora kids from 121 Angora does, a kidding percentage of 325%. When the best procedures are used it seems possible to obtain 5–6 kids from each donor doe (Moore, 1980).
Embryo transfer with frozen embryos has also been used in goats. The techniques used for freezing cattle, goat and sheep embryos are basically similar (Tervit et al., 1972). This requires gradual and stepwise addition of a cryoprotectant at room temperature; the usual cryoprotectants are dimethyl sulphoxide (DMSO) and glycerol but ethylene glycol and propanediol have also been used; the embryos are placed in glass ampoules or straws which are then sealed, placing the ampoule or straw into a programmable freezer which usually cools at -1°C/min to -7°C. At this temperature ice formation is induced in the freezing solution. Cooling them usually proceeds at -0.3°C/min to around -35°C and finally at -0.1°C/min to about -38°C; plunging the containers into liquid nitrogen and storing for varying lengths of time (Tervit, 1983). Thawing usually involves placing the containers into a 37°C water bath until all ice has melted. The embryos are then recovered and subjected to room temperature cryoprotectant removal, either through a gradual decrease in the concentration of cryoprotectant or a sucrose gradient (Niemann et al., 1982; Tervit, 1983).
According to Tervit (1983), in most studies the number of offspring born from 100 embryos transferred is satisfactory. However, embryos found to be degenerate after thawing are usually not transferred (19% rejection rate) and when embryo survival is expressed relative to the number of embryos frozen around 30 to 40% survival appears to be the norm. Only the best embryos are usually frozen (15% rejection rate) and so the extensive culling of embryos pre- and post-freezing means that considerably fewer pregnancies are obtained per embryo collected compared to unfrozen) embryos.
There are different advantages in using embryo transfer in goats: export of genetic material especially where quarantine restrictions prohibit the importation of live animals, or for better adaptation of introduced breeds in new environments, increase in purebred animals and up-grading (Moore, 1980).
Other reproductive techniques
Other reproductive techniques like induction of parturition, early pregnancy diagnosis, breeding at younger ages and induction of multiple births also can be applied in goats, using the same methods described for sheep, but very little work has been done in these areas perhaps because of lack of interest by the goat industry.
SUMMARY AND CONCLUSIONS
Research work around the world has generated a very important technological package of reproductive methods that can be applied to. increase the reproductive efficiency in sheep and goats as a tool for genetic improvement programs. It is possible to synchronize oestrus and/ or manipulate the breeding cycle, increase ovulation rate, control lambing, make early pregnancy diagnosis, breed animals with top quality males by A.I. or build up of stocks rapidly by embryo transfer, etc. But still some of these techniques have to be improved in order to increase the results in terms of lambing or kidding rates The applicability of such techniques are dependent on the structure or system of production in a particular environment and especially on the ecological or environmental restrictions.
Modern reproductive techniques are applied mainly in developed countries but they constitute a very important tool for the genetic improvement of the non-specialized animals in developing countries using the genetic advances made in developed countries. The applicability of advanced reproductive methods in developing countries requires first the improvement of the actual management practices especially those concerned with the animal nutrition, range management and reproductive management. For this it is essential to have a vigorous educational progam including not only technical aspects but also integral education, especially in poor communities like the Indian communities in Peru which own more tha 40% of the total sheep population of the country.
The main research activities for the future that can be identified to increase the reproduction rates in sheep and goats could be the following:
Describe the reproductive potential of the different genotypes of sheep and goats in the different environments in which they are maintained in developing countries (i.e. seasonality of reproduction, ovulation rates, semen characteristics, fertility rates under their current management, etc.);
Evaluate the potentiality of the resources available for sheep and goat production in developing countries;
Introduce modern practices to manage the resources (natural pastures, cultivated pastures, agricultural by-products, etc.) coupled with reproductive methods to increase fertility, fecundity and total productivity of the flocks;
Validate the introduced technology.
In order to improve the actual technology available it will be necessary to;
Continue the research activities to increase the viability and fertilizing capacity of frozen sheep and goat semen;
Development of practical intra-uterine inseminations in sheep;
Optimize the great potential of the immunization methodology for increasing fecundity in sheep flocks;
Improve the fertility rates in out-of-season breeding, especially in goats;
Find a parameter that can be utilized to predict the fertility rate that can be obtained following A.I.
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TABLE 1. Comparison between synchronization methods
|Technique||Approx* cost/ewe (US$)||Ease of Application||Fertility**|
|Vaginal sponges||0.66||+ + +||61|
|PG injection||1.29||+ +||51|
* Excluding labour
** Percentage of ewes conceiving to the synchronized oestrus
Source: Bindon (1982)
TABLE 2. Spring/summer breeding of ewes with progestagens + PMSG
|Location||Month||Technique||n||% ewes lambed||Litter size||Cost/ewe* treated (US$)|
|Ireland||Spring||MAP + PMSG||590||72||1.82||6.00|
|Australia||November||MAP + PMSG||97||60||1.35||2.00|
|December||MAP + PMSG||97||53||1.09||2.0|
Source: Bindon (1982)
* Excluding labour
TABLE 3. Oestrus induction for out of season breeding in Criollo and Junin ewes in the Peruvian highlands using progesterone implants, FGA vaginal sponges and PMSG (400 and 700 i.u.)
|Progesterone Implants||FGA Vaginal Sponges|
|Level of PMSG (i.u.)||400||700||400||700|
|Total ewes treated||9||11||11||11|
|No. of ewes mated (% )||8 (89)||9 (82)||6 (54)||7 (64)|
|No. of ewes ovulating (% )||7 (78)||9 (82)||9 (82)||8 (73)|
|No. of ewes that lambed (% )||5 (56)||6 (54)||4 (36)||6 (54)|
|Lambs born per ewe mated||0.75||1.11||0.83||1.14|
|Lambs born per ewe treated||0.67||0.91||0.45||0.73|
|Lambs born per ewe lambing||1.2||1.67||1.25||1.33|
Source: Vivanco et al. (1985b)
TABLE 4. Results of the immunization against steroids hormones to increase fecundity in New Zealand
|Group||n||Ovulation rate||Dry ewes||No. lambs|
Source: Bindon (1982)
TABLE 5. Results of immunization using the commercial treatment field trials 1982/83 season (Australia)
|Breed||Group||% lambs born||Increse % lambs born due to treatment|
Source: Fecundin* technical bulletin. Wellcome Australia Ltd. (*Trademark)
TABLE 6. Fertilization and pregnancy after insemination with fresh and frozen - thawed semen
|Type of semen|
|Insemination time after sponge removal (hr)||Number of ewes|
|fertilized/ laparotomized (% )||pregnant/ slaughtered (*)|
|Frozen (intra-uterine by endoscopy)||24||7/27||(26)||3/34||(9)|
Source: Maxwell et al. (1983)
TABLE 7. A.I. with frozen semen - Peru
|Semen from Ram №||No. of ewes inseminated by cervical method||Ewes that lambed|
Source: Vivanco and Alarcon (1984)
TABLE 8. Effect of month of A.I. and method of oestrus induction or post A.I. kidding percentages
|Method+||June||July||August – September|
|PMSG + Clo-prostenol||(471)*||(292)||(330)|
|After LLPT||49.0% **||57.2%||58.3%|
+ SLPT = Progestaten sponge for 11 days; LLPT = Progestagen sponge for 21 days
* No. of does
** = P 0.01
Source: Corteel, J.M., Baril, G., Leboeuf, E. and Boue, P. (1984)
TABLE 9. Fertility of untreated goats inseminated with liquid stored semen at different intervals from onset of oestrus
|Hours from first detection of oestrus to insemination||Percentage of does kidding|
|0 – 12||70|
|12 – 24||63|
Source: Corteel, (1981)
TABLE 10. Fertility of untreated goats inseminated with frozen semen in the North Coast of Peru
|Treatment||Percentage of does kidding|
|Inseminated 24 hours after onset of oestrus||67|
|Inseminated 24 and 30 hours after onset of oestrus||72|
Source: Vivanco et al., (1982)