Yak and cattle often share the same habitat, especially during the winter season. It is not surprising, then, that many of the diseases observed in cattle are also reported in yak. From specific studies and surveys it appears that the incidences of some diseases may be high and this is attributed to lack of economic incentive for prevention and treatment in many cases. Incidences of some major diseases have, however, been reduced through strategic anthelmintic therapy and other treatments.
Most of the general literature on yak highlights the remarkable ability of the animals to reproduce and survive in an exceptionally harsh environment and at the same time provide useful products for their owners. The inference might be that the hardiness of the yak also reflects healthiness, in the sense of absence of or resistance to disease. It is important, therefore, to note that yak are prone to most or all the diseases found in cattle elsewhere and that losses associated with such diseases are often quite high.
Information on the insidious losses of production resulting from disease is not readily available, though the economic consequences of such loss could be high. Vaccines and other prophylactic measures, as well as curative treatments, are not widely used even when they are indicated and are known to be effective.
The general paucity of treatment of disease is a consequence of several factors, including the remoteness of much of the yak territory, low cost-effectiveness of treatment (especially as treatment costs may often be relatively high), the traditional nature of much yak keeping and, possibly, a lack of knowledge or recognition of disease by herdsmen. It may also be attributed to the relatively low productivity of yak, which results in limited economic return from any treatment. However, the extent to which these factors apply differs from region to region and among countries with yak.
There are regional and national differences in the inputs of technical and veterinary advice to herdsmen and in the size of yak herds, which has a bearing on whether the products from the herd are primarily for home consumption or are marketed. In some countries and in relation to some diseases, vaccination is provided free by the State.
Many of the disease problems observed in yak may be caused or magnified by stress from the feed deficit in winter and early spring and from weather conditions, including the periodic disasters caused by these conditions. The overall incidence of most diseases is not accurately known for the yak population at large, although authors providing results from specific studies sometimes infer a wide prevalence. Information on some of the disease conditions affecting yak, as reported in a selection of the literature, is summarized in this chapter.
This disease has a long history in China. Herdsmen recognize the clinical symptoms of the disease and its danger to themselves and do not eat the meat of affected yak. Vaccination of yak is used to control it in many areas. Lu and Ling (1985 a, b) recorded in 1958 and 1960 incidences of around 4 percent and mortality of 19 percent in a part of Sichuan and incidences ranging from low to high for areas of Tibet, all with high mortality rates. In Nepal, Joshi et al. (1997) reported an anthrax outbreak that had occurred in the Karnali yak rearing areas during 1990. The outbreak was effectively controlled through vaccination.
This condition is caused by a toxin produced by Clostridium botulinum (type C has been identified in Tibet). Botulism was common among yak in China prior to 1955, but the incidence has since declined. However, Lu and Ling (1985a) recorded 9 193 cases in some counties of Tibet between 1971 and 1979, of which 4 048 were fatal. Vaccination is used as a control in some areas. The bacterium multiplies rapidly in dead carcasses, and it seems likely that the access that yak have to these is accentuated by the custom of disposing of carcass remnants and bones of slaughtered animals on pastures near the campsites of the herdsmen. Carcasses of animals that have died on the range are another source of infection. The yak may become infected either through direct chewing of bones of such carcasses, something they are known to do in cases of mineral deficiency (phosphorus in particular), or the infection may be picked up from polluted water.
Pal (1993) quotes the occurrence of botulism (strains B and C) from several countries with yak.
This infectious disease, which has importance throughout the world, is common among yak and its hybrids. Concern with Brucellosis is made the greater by the fact that it is readily transmitted to humans. In Sichuan, Qinghai and Tibet, sample groups of yak were tested over the period 1952 - 1981, and an average of 17.4 percent (1.8 - 56.3 percent) tested positive (Local Disease Control Office, 1983). Wang and Yao (1984) reported that between 13 percent and 17 percent of yak in various groups on Haiyan pastures in Qinghai province had positive tests and that there was a significant reservoir of Brucella infection among wild animals as well as among sheep and dogs. Yuan (1979) examined 49 Maiwa yak in Honyuan county (Sichuan) by serum agglutination test and obtained six positive reactions. Joshi (1982) also referred to a substantial incidence of positive tests and clinical disease in Nepal and in countries of the former USSR and in Mongolia, but information on the more recent situation in these countries has not been obtained.
In China, S2 vaccine (swine strain vaccine) has been widely advocated for Brucella control measures since 1982. In a study conducted to monitor the effects of the vaccine against Brucellosis in growing yak, Chen and Zhang (1997) tested a total of 9 944 serum samples and 452 samples from aborted foetuses from Guoluo prefecture. The results indicated that the number of Brucellosis-positive samples fell from 21 percent prior to vaccination to 0.4 percent. Brucella species were not isolated from foetal material. Abortion rate in pregnant yak cows also decreased from 18.1 percent before conducting the program in the Guoluo prefecture to 2.8 percent. In a similar study in yak herds in west Sichuan, Pen et al. (1997) reported that the rate of Brucella infection fell from 56.5 to 6.3 percent within four years of S2 vaccination. At the same time, the abortion rate was reduced from 7.4 to 5.4 percent.
Both B. melintensis and B. abortus have been identified as agents with the former the more prevalent in China and the latter more commonly isolated in the former USSR (Joshi, 1982). The strain of B. melintensis found most commonly was Biovar 3, followed by Biovar 2 (Chen, 1983; Peng, 1987). Diagnosis and testing, which depend on laboratory methods, is undertaken mostly for investigation purposes and not for practical yak production.
Vaccination is sometimes used to reduce the spread and prevalence of the disease (noted by Joshi  for countries of the former USSR and for Mongolia) but this practice is not widespread. Testing and slaughter are not considered to be viable options for control - at least not in the present circumstances of yak husbandry. The implications of Brucellosis in yak for human health may require consideration.
In some herds, 30 - 40 percent of calves, particularly the spring-born, develop profuse diarrhoea though this does not necessarily impair the general condition of the animals. The stools are of a thin, pasty to watery consistency, sometimes containing blood. Traditionally, affected animals are given a drink made from medicinal herbs. However, scours in young calves, mostly from birth to four days of age, have also been reported as a major cause of death in two studies with yak. Both studies implicate E. coli. Yan and Ran (1981) reported an incidence of almost 80 percent within the first month of life falling to around 20 percent after that. A report by Lensch (1996) indicates that a mortality rate due to E.coli infection in yak calves was 20 - 30 percent.
In general, recovery rates are high if anti-bacterial treatment is given, but such treatment is not widespread. Tian et. al. (2002) studied the antibiotic sensitivity of 12 antibiotics on 68 strains of E. coli from healthy yak. Results showed that acquired drug resistance of E. coli was not a problem in yak in Qinghai as antibiotic use is not common (see section, Viral diarrhoea / mucosal disease).
Contagious bovine pleuropneumonia
This disease is caused by Mycoplasma mycoides and occurs among yak, between two and ten years old, principally in winter and spring when the animals are more closely confined than in the summer. In one such period, Hu et al. (1960) recorded an exceptionally high incidence of 54 percent in Ganzi county of Sichuan province. Lu and Ling (1985a) reported an incidence of 1.9 percent for herds in Tibet and a mortality of around 17 percent among those affected. Though vaccination is an effective option for control, it is not widely practised.
Relatively recently, Chlamydia infection has attracted attention because of the apparent susceptibility of yak. Wang (1990) examined 102 yak and found the incidence to be 10.8 percent. In another report, Yuan (1991) showed an incidence of 42.7 percent among 553 yak. Shuai Yongyu et al. (1988) reported that abortions in yak in a part of Qinghai province were diagnosed as caused by Chlamydia psittaci infection. Tests on serum samples collected from yak that had aborted showed positive tests in 45 of 155 samples. Ma (2002) conducted a study to monitor the prevalence of Brucella and Chlamydia in Qinghai province. Out of 526 samples screened, only one sample was positive for Brucella and 15 samples were positive for Chlamydia, indicating that the incidence of abortion in yak due to Chlamydia may be of significance.
These studies show in respect of this form of abortion, as for many diseases, that yak are susceptible and that the infection exists in yak-producing areas. They do not indicate the overall incidence of the disease in that area of the country, or whether it is prevalent elsewhere.
This disease, which causes a generalized but serious illness in yak, was reported to have occurred in parts of Sichuan in the period 1980 - 1982, according to a report by Cheng et al. (1985). These authors recorded an incidence of 10 - 20 percent and a mortality of 30 - 50 percent. Agglutination and complement fixation tests on 187 serum samples were positive in 53 cases. Vaccines have been tried against the disease in the former USSR, but results were not satisfactory (Nivsarkar et al. 1997).
Lymphadenitis can cause severe economic loss among yak. Multiple, hazelnut- to walnut-size abscesses appear on the skin of the neck and lower jaw and eventually rupture. They interfere with the animal's ability to feed with resultant loss in weight. Treatment in the primary phase with penicillin and streptomycin has yielded good results (Kosykh, 1964). Joshi (1982) reported serious economic loss from the disease in Nepal but quotes a report from southern Buryatia in the 1960s where the incidence appeared even more serious. Sporadic outbreaks of this disease have also been reported to occur among yak in Russia (Lensch, 1996).
Mastitis occurs in yak, but it is believed that the incidence is less than among dairy cattle, perhaps on account of the relatively low milk yield of yak and the suckling of calves. An outbreak in Hongyuan county of Sichuan was reported by Weggi (1983) to be due to streptococcal infection and similar in epidemiology, clinical symptoms and in response to medication to that found in cattle. The outbreak affected some 10 percent of the yak recorded by Weggi and coincided with a period of hot, dry weather and overcrowding on pastures at that time.
Joshi et al. (1997) reported that in a study of mastitis in yak herds in Nepal, the bacteria isolated from the milk were mainly Staphylococcus aureus, Streptococcus agalactiae and other Streptococcus spp. and Coliform spp.
This disease is reported to occur every year in yak-producing areas and takes the form of a haemorrhagic septicaemia. Lu and Ling (1985a) noted in parts of Tibet between 1976 and 1979, a 0.34 percent incidence of haemorrhagic septicaemia among yak, with a mortality rate among affected animals of nearly 36 percent. A higher incidence of 2.3 percent with 89 percent mortality among animals in Baiyu county (Sichuan) was reported by Yang (1987). Joshi (1982) noted the occurrence of haemorrhagic septicaemia among hybrids of yak with local cattle in many districts of Nepal but made the point that these were in the lower and middle hill regions where the disease can be virulent and result in high mortality and that the incidence was much more limited in the higher alpine areas. Pal (1993) also quoted the occurrence of the disease among yak in India. Nivsarkar et al. (1997) reported that mass vaccination has effectively controlled the disease in other livestock species but has been little used in yak.
The disease is common among yak in China, mostly among calves between 15 and 60 days of age (S. typhimurium, S. dublin and S. newport have been isolated). Between 1960 and 1980 an incidence of 40 percent, with a mortality rate of 35 percent, was recorded for five counties of Gansu province (Lu, 1986). Similar studies from 25 counties in Tibet (1976 - 1979) recorded 5.2 percent incidence and 26 percent mortality (Lu and Ling, 1985a) and 10.5 percent incidence with 56 percent mortality in Qinghai (Deng, 1983). Effective vaccines have been produced in several of the Chinese provinces but are not widely used by the herdsmen.
Tetanus occurs occasionally in yak breeding areas. Ma and Kang (1993) reported that during 1959 - 1989, 32 yak suffered from tetanus and 31 of them died. The disease has been under control recently because of improvements in yak management.
Yak are susceptible to the bovine strain of Mycobacterium tuberculosis. Although the disease is known to occur in yak, there is little quantified information available and no control schemes are in place. Lu and Ling (1985a) tested 1 749 yak in Tibet with a single intradermal test and found that 12.7 percent of animals reacted positively, but some of these showed no other visible lesions. In Nepal, out of 23 tuberculin tests conducted in yak, three were found positive (Joshi et al., 1997).
Other bacterial diseases
Other bacterial diseases reported for yak include Blackquarter (Joshi et al. 1997), Coxiella burneti infection (Geilhausen, 2002), Kerotoconjunctivitis and Camphylobacterosis.
Foot and Mouth disease
This disease was well known in yak in the past. In 1960 an outbreak was recorded in Ganzi county of Sichuan with an infection rate of 72 percent and a mortality rate of about 4 percent. Strain O caused the highest mortality. Joshi (1982) and Joshi et al. (1997) reported a number of outbreaks in different parts of Nepal among yak and hybrids of yak with local cattle. They state that quarantine of affected animals is used in alpine regions of Nepal with the intention of allowing the lesions to heal and that vaccination, though effective, is not widely used. Pal (1993) referred to an outbreak in Sikkim in 1973 caused by the virus of strain A. Prasad et al. (1978) reported an outbreak among yak in the state of Himachal Pradesh. A virus of strain O, previously reported from Nepal, was isolated in that outbreak.
Infectious Bovine Rhinotracheitis
The Infectious Bovine Rhinotracheitis is caused by a herpes virus and can cause abortion in severe cases. Qu and Li (1988) tested 126 yak serum samples with 45 samples positive to ELISA and 44 positive to the neutralization test.
Yak are highly susceptible to Rinderpest with reported mortality rates of 90 - 100 percent. In China, the disease has been eradicated through vaccination since 1955. Prior to then, the disease was widespread (Liang Daxin, 1948); around one million yak are said to have died of it between 1928 and 1941 in the provinces of Qinghai, Gansu and Sichuan alone. A further outbreak in Qinghai in 1944, also reported by Liang Daxin, claimed 20 000 yak within seven months. Joshi (1982) refers to outbreaks with mortality rates up to 90 percent in parts of Nepal prior to 1966. Vaccination programmes, such as those in Mongolia and in the former USSR, as in China and elsewhere, may well have brought the disease under control.
Viral diarrhoea/mucosal disease
Gao et al. (1999) collected serum samples from yak herds in the pastoral regions of the northwestern and southwestern provinces of Shaanxi, Gansu, Ningxia, Qinghai and Sichuan for the detection of antibodies against bovine viral diarrhoea/mucosal disease (BVD/MD). The authors found that the detectable rate of BVD/MD in yak herds reached 30.08 percent, with the infection rate of Sichuan yak herds the highest (38.46 percent), followed by Gansu (29.41 percent) and Qinghai (28 percent).
Other viral diseases include pox and rabies (Joshi, 1982); Vesicular stomatitis (Lensch, 1996); calf diphtheria and arthritis (also listed, unusually, under viral diseases) (Joshi et al., 1997); parainfluenza 3, bovine Herpes virus 1 and bovine diarrhoea-mucosal disease are also reported to occur in yak (Geilhausen, 2002).
Ticks, fleas, lice and mites
These have all been found in yak, though herdsmen do not, in general, recognize their importance or the irritant effect on the animals.
Ticks: A report by Biswas et al. (1994) documents infestations with ticks of five genera, among yak is tracts of Arunachal Pradesh of India and lists the types found and the sites os infection on the animal. According to Lensch (1996), ticks cause moderate to severe infestation in cattle and yak on grassland in all regions of Mongolia. Clinical symptoms in severe infestations include restlessness and anaemia. Referring to yak in Mongolia, Lensch and Geilhausen (1997) wrote: "Ticks are found on the animals' eyelids, in the outer ear, on the cranial side of the neck and on the anterior and posterior thighs. Tick infestation is at its height in the rainy season from May to September. Ecological planning is recommended for tick control and should take into account seasonal variations, range of hosts, and known infected areas. The traditional method used by Mongolians of moving the cattle and yak to more or less tick-free grazing land during the summer months, largely protects the animals from (heavy) tick infestation." Joshi (1982) also referred to ticks among yak in Nepal and draws attention to the possible disease transmission caused by them there.
Fleas: when they occur, are found on any part of the yak's coat. As recorded by Lensch and Geilhausen (1997), the fleas "sometimes occur in conjunction with ticks on grazing land. The clinical symptoms are pruritus, anaemia and localized skin damage."
Lice: The report of Biswas et al. (1994) also provides evidence of infestation by lice of one genus in Arunashal Pradesh. There are apparently on report of this parasite in yak from elsewhere.
Mites: of a number of different families have been recorded in yak and yak hybrids in Nepal (Joshi, 1982). The main families are Psoroptidae and Sarcoptidae and cause the disease commonly called "mange". The clinical symptoms are persistent itching and chronic inflammation of large areas of the skin, especially of the back. Like in Nepal, Yu also observed mite infestations of yak in China (mainly yak calves of one to two years old).
This disease is caused by Babesia bigemina a protozoan parasite. In Aba prefecture of Sichuan province in 1981, 549 cases of yak infected with the disease were found and 273 of them died. In 1985, the disease broke out elsewhere in Sichuan province where around 500 yak died from it (Yu et al., 1989). The organism is transmitted by ticks, and the symptoms are fever and haemoglobinuria.
Yak hypodermiasis (warble or gad fly)
On the basis of a study by Wang Yanhong (1994), yak hypodermiasis is a significant problem in yak. Jiang et al. (1997) reported that out of 1 149 yak examined in Sichuan province, the parasite rate of hypoderma larvae was 84.2 percent. Young yak between one and three years old were reported to be the more susceptible. Three varieties of Hypoderma, namely H. bovis, H. lineatum and H. sinese, have been identified, with H. lineatum the most prevalent, accounting for 70 - 80 percent of all cases (Jiang et al., 1997).
Larvae from warble fly (gad fly), cause damage to the skin as they burrow into and emerge from the hide, particularly on the back and loin of the yak. Apart from physical damage to the hide and loss to its value, there is irritation to tissues and secretion of toxins that retard growth and development in young yak and reduce milk yield and meat yield of adults. Death results in severe cases. Intramuscular injection of a vermicide (Ivomec) was fully effective in killing the larvae. In one trial, 110 out of 2 393 untreated yak died, but out of 500 that had been injected with Ivomec, only 2 died; the treated yak were also in better condition (Jiang et al., 1997).
Lensch (1996) (basing his information on the personal communication of a study attributed to Minarz and Dorz, dated 1970) wrote that, in that study, 96 percent of adult yak and all juvenile yak examined were infested with H. bovis with infestation rates of 11 larvae per day in adults and 40 per day in young animals and that up to 280 larvae were found to be present in yak calves.
Also according to Lensch (1996), at the much higher elevations in Tibet (relative to Mongolia) fly strike usually remains untreated. Lensch (1996) also wrote that there appear to be no scientific reports of warble fly infestations from Bhutan, India or Kyrgyzstan; he noted, however, that in Mongolia, as in some parts of China, economic loss from warble fly attack in yak could be very serious if an intensive control program were not in place.
Gid disease (Coenurosis)
Samdrup (1992) provides evidence that gid (Coenurosis) is a parasitic disease of economic importance for yak herdsmen in Bhutan. The cause of death is the intermediate stage of Coenurus cerebralis of the tapeworm Multiceps. The adult form parasitizes canines, including dogs, wolf, fox and jackals. Watchdogs, which are kept by herders to control and protect their yak from wild carnivores, are the main intermediate hosts in Bhutan. Yak become infected by grazing on pastures contaminated by dog faeces containing Multiceps (Tenzin, 1979). About 70 percent of the gid cases were reported in young animals of one to two years old (Tenzin, 1979). An eradication programme for gid was introduced consisting of deworming yak calves with Albendazloe and Fenbendazole and dogs with Niclosamide. As reported by Wangdi (1996), the programme was successful in reducing yak mortality due to gid in yak herds in one of the worst-affected areas of Bhutan from 40.3 percent in 1992 to 1.5 percent in 1994.
In a survey conducted to investigate the presence of hydatid cysts among 50 yak in Sikkim, 80 percent were found positive for the cyst (Ansari and Rai, 1991). In China, the incidence of hydatid cysts in the 535 Gannan yak examined was reported to be 41.8 percent (Li et al., 1985). Joshi et al. (1997) reported on a similar disease condition due to tapeworm of Echinococcus spp. in Nepal yak.
This is a common occurrence in yak in China and elsewhere where wet conditions exist. It is caused by Fasciola hepatica and, from an economic point of view, is one of the most important diseases in yak, as it considerably impairs the animal's performance. Infestation rates of 20 - 50 percent are common, though a study by Shuqiu Cheng et al. (1994) refers to infestation rates up to 80 percent of yak in some grassland areas. Lensch (1996) noted that risks of liver fluke infestation are greatest at altitudes below 3 000 m and that in northwestern Tibet, at elevations between 4 500 m and 6 000 m, fascioliasis seemed to be of no importance. Zhu and Jiang. (1986) collected more than 7 000 snails in three areas of Sichuan and found the principal host snail to be Galba pervia. Herdsmen try to control infestation by restricting grazing of yak on marshland in the spring to only half a day at a time and to prevent access to marshland after rain. Marshlands are also burnt in winter. Dosing with triclabenzadole is effective in yak (Zhu and Jiang, 1986), but the extent to which it is used is not recorded.
Joshi (1982) noted significant infestation by liver fluke of both yak and their hybrids with cattle in many villages in Nepal. Out of 100 yak faecal samples tested in Nepal, 58 were reported positive for the presence of liver fluke eggs (Joshi et al., 1997).
A report by Liu (1994), from studies in Tibet, suggested that roundworm infestations and the associated larvae may be a common problem in yak, though not as extensive as among the sheep on the same pastures. Many genera of roundworm were isolated (and listed by Liu, 1994), but the prevalence of different genera varied with the time of year. Liu (1994) noted that routine antiparasitic treatments were restricted to government yak farms and a few selected private farms but that the majority of yak were not involved in any treatment programme because worm infestation does not cause visible symptoms that might alert yak herders to a problem.
Wangdi (1996) examined faecal samples collected at random from 26 adult yak and 81 yak calves from western Bhutan. The results showed that in the adult yak, 19 percent were positive for Strongyle spp., while among the calves 37 percent were positive for Strongyle spp., 2 percent for Coccidia spp. and also 2 percent for Trichuris spp.
Pal (1993) quoted one study on yak in Sikkim showing 62 percent of yak infected with helminths. Another report based on a study conducted by the National Research Centre on yak in India in 1995 indicated that of the 63 yak faecal samples examined in Arunachal Pradesh, 32 were positive for various helminth eggs (Trichuris, Strongyles, hookworms, Dicrocoelium and Ascaris).
Contagious skin diseases
Various contagious skin diseases, including ringworm (attributed to the fungi Trichophyton and Microsporum) and a chronic dermatitis, caused by the bacterium Dermatophilus congolensis, are also reported to occur in yak.
Pyrrolizidine alkaloid poisoning
Large numbers of deaths among yak in one part of Bhutan were found by Winter et al. (1992, 1994) to be due to Pyrrolizidine alkaloid poisoning. Several toxic plants were found to be involved, with species of Senecio predominating. It was concluded that the yak had been induced to eat these plants, which they would normally avoid, due to hunger arising from overgrazing of the pastures concerned. This matter is also referred to in Chapters 8 and 13).
Yak can die suddenly or after protracted illness after drinking water from stagnant ponds, marshy areas and potholes (Dahl, 2000). The cause of the problem is not fully explained. This is a common condition in yak in Bhutan. The stagnant water appears red and oily and covered with greenish surface scum. A surprisingly high mortality rate of 39 percent was reported from a yak herd in central Bhutan (Sharma, 1996). In a separate study conducted in central Bhutan, Dorji (2000) reported that 37 out of 130 yak deaths were due to "poisoning" from contaminated water. Death occurs, especially during the onset of the winter season, when the yak return to their winter pastures. Although conclusive evidence could not be established, analyses of water samples collected from the affected areas have revealed the presence of blue green Cynobacteria algae (Dahl, 2000). Provision of an antidote, comprising activated charcoal and magnesium oxide (which can adsorb a variety of toxic chemicals) and broad-spectrum antibiotics, if administered in the early phase of the disease, was reported to be beneficial.
Mineral and trace element deficiency
Problems of mineral or trace element deficiency or imbalance are not specifically reported in the literature from yak-producing countries. An observation from Whipsnade Wild Animal Park in England (where a small herd of yak have lived since the 1940s) indicated that the yak there showed several of the symptoms of copper deficiency on the same diet that other Bovidae, and local domestic cattle in particular, find adequate, or nearly so, in respect of copper content (Nick Lindsay, Curator, and Edmund Flack, veterinarian at Whipsnade, personal communication, 1994). Copper supplementation of the yak diet and occasional copper injection has brought improvement in the health, vigour and performance of the yak (Edmund Flack, personal communication, 1994). This suggests at least the possibility that yak may have an inadequate copper uptake due to an inherently low capacity of yak to absorb dietary copper - because a genetic component to the uptake of copper is well documented in other species (Wiener, 1987). More recently, Claus and Dierenfeld (1999) have reviewed and discussed the topic and provided more evidence of copper deficiency in captive yak.
Copper deficiency can result in poor growth and poor fertility, among other symptoms - but poor growth and poor fertility, by themselves, do not necessarily indicate copper or any other mineral or trace element deficiency, as overall poor nutrition may be the cause of the problem. In actual mineral and trace element deficiencies, appropriate supplementation will generally improve the conditions caused.
Inherent remoteness and inaccessibility of the yak-rearing areas makes the delivery of conventional health services difficult. Because of this, herdsmen have acquired special local knowledge to deal with various livestock diseases by themselves.
Jest (1975) reported that yak are often bled from the jugular vein or the underside of the tail to provide blood for human consumption (originally for the benefit of the local people but now [Corneille Jest, personal communication, 2002] developed into a lucrative "industry" to cure gastric ills (such as among the Thakali in northern Nepal). However, the herders also claimed that this practice had benefits for the animal by "fortifying" it and renewing its old blood (see also Chapter 10). Craig (1997) provides information on traditional healing techniques, said to include principally moxa treatment (moxibustion) and bloodletting, practised by the local healers in Mustang and by Dolpo yak herders of Nepal and claimed as a cure for lameness and to "fortify" the yak.
Dorji and Tshering (1999) reported on diverse uses in Bhutan of herbal preparations and traditional healing methods for ailments such as Foot and Mouth disease, Blackquarter, plant and water poisoning, fractures and parasitic diseases. Hu Songhua (2002) describes four herbal prescriptions (Powder of Dandelion, Decoction of Snakegourd and Burdock Achene, Ease Powder and Decoction of Eight Precious Ingredients) and acupuncture methods for the treatment of bovine mastitis.
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 Tashi Dorji Livestock
Programme Officer at the Renewable Natural Resources Research Centre, Ministry
of Agriculture, Jakar, Bumthang, Bhutan;|
 Walter Roder is advisor Agronomist at the foregoing;
 Professor Yu Sijiu is Dean of the Faculty of Veterinary Medicine Science, Gansu Agriculture University, China