M.R. Goe and G. Stranzinger
Department of Animal Sciences, Swiss Federal Institute of Technology, Tannenstrasse 1, CH-8092 Zurich, Switzerland
This paper briefly reviews breeding systems used for domestic yak and for yak hybrids. Traits for production and performance commonly selected by herders for breeding are highlighted. A simple recording system is then proposed that would allow breeding activities to be jointly monitored by herders and extension workers to reduce the presence of less desirable traits in herds and improve overall production and performance. The system would also permit basic information to be gathered on herd structures which can assist researchers and livestock extension workers to determine the extent of inbreeding within regions or areas of a country and better plan for appropriate interventions.
Keywords: Herd recording, inbreeding, trait, yak, yak hybrids
Miller and Steane (1997) reported the distribution of domestic yak and yak hybrids as including the high-elevation areas of the Hindu Kush and Karakoram in Afghanistan and Pakistan; the Himalayas in India, Nepal and Bhutan; the Tibetan Plateau and Tien Shan mountains of north-western China; and western and northern Mongolia. Yak are also found in the adjoining areas of Russia and some of the central independent states of the former U.S.S.R. These animals provide pastoralists and agro-pastoralists living in these areas with a number of products (milk, meat, hair, hides and manure for fuel) and services (draft, packing and riding). They also serve important socio-economic (financial security) and cultural functions (status, dowry, religious festivals etc.).
A review of the papers presented at the two previous international congresses on yak (Rongchang et al. 1994; Rongzhen et al. 1997) and of the information contained in two key publications (Cai and Wiener 1995; Miller et al. 1997), as well as various other sources in the literature, indicate that inbreeding in the yak is of major concern, not only in terms of the adverse effects it can have on animal production and performance, but also its impact on genetic diversity. In this paper, general breeding systems and traits selected for production and performance by herders are briefly described. A simple recording system is then proposed which herders and extension workers could use as a start towards monitoring breeding activities at the herd level. The system will provide a tangible means by which herders can better differentiate among their animals, and thereby, justify their estimated value for production, performance and market. Additionally, the system will facilitate the collection of baseline information on herd structures that can assist researchers when using modern diagnostic methods to evaluate or measure genetic diversity within populations. Information on herd structures can also be useful to livestock planners to determine appropriate interventions during disease outbreaks or natural disasters such as drought or severe winters.
Herders traditionally breed yak or cross them with cattle to obtain offspring having traits that will maintain or enhance production and performance, in order to support their subsistence livelihoods and produce a commodity for existing markets. Strong emphasis is placed on producing offspring that are adapted to, and can survive in, the harsh environments in often-rugged terrain in the mountainous regions.
It is not within the scope of this paper to give a detailed discussion of all the breeding systems used by herders within and among different countries. However, the three systems described by Tshering et al. (1997) for Bhutan can be considered as being generally representative of systems used in other countries. The systems are: 1) pure line or straight breeding in which yak bulls (exchanged between breeding areas to avoid inbreeding) are mated with yak cows; 2) crossing of yak bulls with Bos taurus and B. indicus cows and their hybrids; and 3) B. taurus and B. indicus bulls are crossed with female yak and their hybrids. Modifications of this system, along with information on different criteria for culling of animals and various schemes of backcrossing, can be found in several reports (Cai and Wiener 1995; Miller et al. 1997; Rongzhen et al. 1997; Wu 2000).
Herders attempt to improve performance traits of offspring through selection of bulls or females having those traits deemed important based on traditional knowledge and experience. In Nepal and Mongolia, for example, herders select breeding stock for preferred colours, markings and other characteristics including size, conformation, horn shape, milking ability and behaviour patterns (Joshi et al. 1994; Davaa 1997). Similar traits are considered in a list of traditional selection criteria for Jiulong yak compiled by Wu (1998), Wu (2000) based on Cai (1989) and Cai and Wiener (1995).
Yak are thought to have been first crossed with Chinese yellow cattle more than 200 years B.C. (Rongchang et al. 1994). Hybridisation of yak and local/native or exotic cattle is carried out to obtain the benefit of heterosis in producing females with higher milk yields or larger animals for beef production or draft. Crossing of yak with one or more exotic cattle breeds (including Angus, Brown Swiss, Charolais, Hereford, Holstein, Jersey, Murray Gray and Simmental) has been carried out in most of the central Asian countries where yak are native (Paudyal 1986). Yak hybrids in Nepal are reported as being better adapted to the intermediate zone between cattle and yak habitats and are, therefore, able to utilise grazing areas too low in elevation for yak, but too high for cattle (Robinson 1992, cited in Joshi et al. 1994). Male hybrids are commonly used for work. In China, for example, first crosses of yak females are mated with local bulls and the reciprocal crosses are widely used for draft or packing (Cai and Wiener 1995).
The crossbred F1 of either sex is widely accepted to be superior to its parents in terms of growth and productivity. However, a drawback commonly cited is that crossbred animals are less adaptable to environments in higher elevations, especially during winter when supplements are required (Rongchang et al. 1994; Wu 1998). Shijian and Weisheng (1997) reported that hybrid F1 offspring are not resistant to the harsh conditions over 3000 metres above sea level (masl). Joshi et al. (1994) stated that in Nepal F2/F3 offspring have little value and are usually slaughtered shortly after birth, whereas in India, farmers tend to keep animals belonging to F2/F3 generations, and F4 onwards, although they are less productive and, therefore, not remunerative (Pal et al. 1994). Hybridisation may not be practised in certain areas, due to hybrids carrying the stigma that the milk and meat is of inferior quality to pure yak, and male offspring are infertile (Gyamtsho 1996; Tshering et al. 1997). Yak hybrids (F1 and subsequent generations) are reported to produce less undercover or fine hairs (Pal 1997). Selection traits for animals to be mated will depend on projected use of offspring, but are similar to those mentioned for yak. Bulls used for hybridisation with female yak should have a high production potential, but be of smaller size to avoid calving difficulties (Pal et al. 1994).
As with any species, proper breeding practices are necessary to maintain or improve levels of performance (milk and meat production), reproduction, suitability for work (draft, packing and riding), fitness (stamina) and disease resistance. However, use of the same yak male for several years to breed the same females, or hybridisation of yak with cattle through a number of generations beyond F1 is not uncommon (Pal et al. 1994). Despite herders' intentions to employ sound breeding methods, this is often not possible. Replacement for males are normally chosen from among the sons of the currently used bull, generally from his own herd or from a relatively small group of herds with which he is associated. Competition among bulls for females results in the most aggressive and fertile male siring the most offspring. This process inevitably leads to inbreeding. The rate of inbreeding is likely to be more rapid in small herds or small herd groups using fewer bulls than larger herd units (Wiener 1997). Additionally, one has to recognise the herder's approach to breeding from a practical standpoint. His or her goal is to obtain as many new calves per breeding season as possible, even if an animal does not possess the desirable level of heterozygosity, which does not imply that it is not an economic investment (Pal et al. 1994).
Numerous papers highlighting the problem of inbreeding in yak herds can be found in the documents cited earlier. Inbreeding has been reported as being a particular problem in Bhutan, Nepal and India, whereas in the Hunza region of Pakistan and remote areas of Afghanistan, herds are thought to be less inbred (Cai and Wiener 1995). Miller and Steane (1997), although recognised that inbreeding exists in certain yak populations, caution that additional studies and more accurate data are required to better assess the extent to which inbreeding poses a problem in countries and in which specific areas or pockets.
The main impact of inbreeding is reduced heterozygosity at the animal and herd level, resulting in lower animal performance. Adverse effects can be readily observed in terms of an animal's physical size and conformation. Inbreeding can produce animals lacking the stamina to survive in harsh environments and extreme temperatures at higher altitudes, particularly during winter months. Improper mating can result in development of overly large or deformed udders, making females more prone to injuries and reducing suckling or milking ability. Additionally, inbreeding can cause a lack of pigmentation around the eyes or on the mussel, leaving animals without protection against the effects of solar radiation. Use of overly aggressive sires can result in offspring being predisposed to fighting, increasing the risk of injuries to themselves and others. Aggressive animals are more difficult to handle, making them less suitable for work, thereby resulting in a loss of potential income from draft or packing.
Artificial insemination (AI) has been used successfully in some countries, notably China, on-station or in the rural areas surrounding larger population centres to reduce inbreeding in yak populations. However, establishing AI facilities and services is not easily done in remote areas (Shijian and Weisheng 1997). In India, it has been recommended that AI be employed where possible using semen from China and that more consideration be given to herd structure, use of better breeding bulls and specific breeding programmes focusing on specific traits (Pal 1997; Pal and Madan 1997). Ultimately, the extent to which AI is used to reduce inbreeding in different countries will depend on the existing circumstances, particularly, the human and financial resources, and infrastructure to support AI. Although embryo transfer has been suggested as a means of improving genetic diversity in yak (Davaa 1997), its use will continue to be limited in the near future due to cost and specialised infrastructure and sanitation requirements.
It maybe worthwhile to mention that inbreeding also poses potential problems in countries where yak rearing is not traditionally carried out. Yak are being raised in Europe, Canada and USA on a very small scale (probably less than a total of 2000 animals) mainly for meat, and to a limited extent as pack animals for trekking, and some fibre production. There are also a few yak herds in Germany and Switzerland. Access to financial resources alone is not enough to ensure that inbreeding does not occur. In Switzerland owners have the money to import semen or embryos, but this is prohibited by law (Daniel Wismer, personal communication). In Canada and USA there are currently 72 registered yak breeders. Bulls are exchanged between herds to prevent any more inbreeding than has already taken place. AI using semen from the registered herds is not widely practised. Government regulations currently prohibit the importation of semen from China and elsewhere (Phil Wykle, personal communication).
Herders are probably the single most important factor to be considered when making efforts to reduce inbreeding in yak. As noted by Ning et al. (1997) and Wu (1998), pastoralists' societies have both the traditional knowledge and skills to improve the production characteristics of their yak and have established procedures for selection of animals. It is widely accepted that this type of information needs to be collected and incorporated into programmes aimed at reducing inbreeding. For a programme to be sustainable, the herder must be fully integrated into the process, understand why information is being collected and how it will be used, and be able to see the tangible benefits to be realised by participating. One possible way to begin this process would be to introduce a simple means of recording information on parentage, management and production and performance traits of animals in the herd (Table 1). Herders and extension workers, in consultation with researchers and livestock advisors, can further develop the card to include other information as necessary. Attributes or traits deemed important by herders can be added to the basic data recorded for each animal. A copy of the card would be kept with the herder and a copy with the recorder. Periodically, the information would be transferred to the responsible institution for data entry, analysis and evaluation.
Use of such a system to monitor breeding activities within and between herds will allow participating farmers to better evaluate animals when making selections for mating. Individual record card would distinguish between those animals having certain desired production and performance traits and those that do not. Because farmers owning these animals are part of a recognised performance recording programme, their animals are likely to be viewed as being more valuable (Schneider et al. 1999). One goal of such a recording programme would be to reduce inbreeding within herds. However, even if inbreeding does occur, there would at least be a record of it. By having access to such information, extension workers, researchers and livestock planners can better identify areas or regions with more acute inbreeding problems and, where possible, take appropriate action. The system could be developed and expanded to include monitoring of animals of different breeds and from different areas, in order to provide a basis for identifying locations for carrying out studies to gather information on genotype-environment interaction (Weiner 1997).
It is recognised that there are numerous obstacles one faces when trying to introduce such a recording system, notably lack of finances, infrastructure and trained personnel. However, these are not insurmountable (Trivedi 1998). Rather, the key factor will be to gain the trust of the herders so that they will actively and fully participate. In this regard, previous contact with herders can be an advantage in introducing such a recording system. For example, herd or farm surveys have been carried out in India (Pal and Madan 1997) and in Tibetan Autonomous Region, P.R. China (Ruijun et al. 1994). Organisational support could be given to herders in different yak-rearing areas to form breeder's associations or groups. Associations such as those, which exist in Xinjiang, China, could be used as a model. Herders and officials have established breeding methods for identifying entire groups of yak, eliminating inferior animals from the breeding pool and establishing core breeding groups (Ning et al. 1997). Sherchand and Karki (1997) proposed group-breeding schemes in Nepal. Building on these and other experiences will facilitate the introduction of such a recording system in new areas and support its development in others.
Table 1. Yak record card.
|Name of Herder|
|Breeder's Association (Group)|
|Location (region, country, district)|
|Name of Extension Agent|
|General Animal Identification|
|Breed or Type|
|Other (purchased, traded, etc.)|
|How long in herd|
|Packing or transport|
|Age first used for breeding1|
|Reason for use|
|Date first bred2|
|Age at first calving1|
|Sex of calf|
|Lactation length (days)|
|Average daily yield (kg)|
|Date of removal2|
|Reason (sale, death, etc.)|
|Incidence of diseases|
|1. Months/years. 2. Season/month/year.|
In addition to production and performance goals, political or economic factors can also have an impact on breeding management. The closing of borders between Tibetan Autonomous Region and Nepal, which severely reduced animal movement, has been attributed to causing inbreeding and negatively affecting yak production (Joshi et al. 1994). Given the recent change in the border situation, more opportunities to introduce new blood lines into Nepal, either by importation of yak males for natural mating or through AI, are likely to become available. Thus, the need to monitor breeding activities and herd structures in areas along the frontier will become increasingly important.
One can expect to and also see a gradual shift away from traditional production systems to more commercially oriented ones as previous income generating opportunities for herders change and new ones develop. In the major trekking areas of Nepal, yak and yak hybrids are increasingly being used for trekking and mountaineering expeditions, thereby transforming the structure of herds in some areas to a much higher percentage of pack animals (Joshi et al. 1994). The continued popularity of these expeditions is likely to result in Nepal and neighbouring countries exploiting such tourist activities to earn more foreign exchange. Under such situations, herders will quickly recognise the potential income to be realised from producing pack animals and modify their breeding practices accordingly.
While research stations and government farms can play a positive role in developing potentially viable breeding and selection strategies, long-term and sustainable improvements can only be realised at the herder or farm level. The recording system proposed here, albeit simple, can promote the involvement of herders in gathering baseline information, which is currently lacking on herd structures and breeding management. The system is flexible and can be modified as required. Outputs will lead to improved yak production and performance, and contribute to breed sustainability and genetic diversity.
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