Ways of improving yak productivity by selection might be of great importance to the people who depend on yak for their livelihood. As discussed earlier, the yak is the dominant domestic animal in the alpine regions and the mountain plateaux of western China and adjacent areas to the south and north – dominant in economic, though not necessarily in numerical, terms.
The Important Of Yaks
The yak also has great importance in Mongolia and several other countries. It is an integral component of the socio-economic system of people in many remote areas and, often along with sheep and goat, it is the main contributor to the livelihood of the herdsmen and their families. And yet, several factors militate against systematic breeding programs.
The first of these constraints on improvement by genetic selection is that yak are still widely regarded, especially among Tibetan people, as a symbol of wealth. The more yak a family or a village owns, the richer and stronger it is considered to be. To maintain or increase the number of yak can take precedence over improvements in quality, or even overall productivity.
Thus, animals are often kept until they die rather than culled for reasons of poor productivity. This can lead to overstocking of pastures and to a potential reduction in the output from the herd as a whole. “Quality” of the herd can become more of a consideration in situations where “competing” families or villages already own similar numbers of animals. Observation also suggests that smaller herds are sometimes of better quality because more pasture resource is available for a given number of animals and greater individual care is given to the animals by the herders.
A second important reason why genetic selection by herdsmen, or by extension officers acting on their behalf, is impeded is the absence of the necessary performance and parentage records – although herdsmen will often claim to know the parents of yak, especially bulls. It is doubtful if the accuracy of this knowledge is ever tested. In some nucleus breeding herds set up recently on the state farms in Qinghai, Tibet, Gansu and Sichuan, pedigrees but not performance were recorded.
Third, survival of the yak in a harsh, even hostile, environment is of paramount importance, perhaps of higher priority than any other single performance trait (though it is unlikely that this matter has been quantified). In terms of selection for survival under these conditions, natural selection is almost certainly more effective than any current procedure devised by man.
In relation to selection for the main products from the yak – milk, meat and fibre – the only convincing evidence of changes resulting from selection applies to fibre, where selection of a “fibre line” in the Jiulong breed appears to have produced far higher yields than in contemporary animals not selected for this trait. Because fibre traits are quite strongly inherited and much more so (at least in other species) than milk yield or growth traits, selection progress is relatively easier to achieve with fibre production traits.
The milk yield of yak is very low, relative to other cattle, particularly those specializing in milk production. It has been suggested that the amount of milk produced by yak is only the quantity that would normally be needed to rear its calf. Thus, yak calves that receive only some of their dams’ milk, because the rest is taken for human consumption, grow significantly less well. An incentive to select for a higher yield in yak is most likely to arise only where there is an expanded market for milk destined for sale.
In respect to meat output from yak, three problems arise that may create conflict with opportunities for selection for growth rate or “size” (meat production), even if these traits were somehow measured. One is the fact that a significant proportion of each year’s growth of the animals during the warm season is lost over the period of nutrient deficiency in winter and early spring.
This makes it difficult to see what an appropriate selection strategy should be. If the strategy were to be the increase in the size of the adult animal, say at the end of a growing season, the selection process would be delayed to late in life and hence would make slow progress. A second constraint is that when milk is taken from yak for human consumption and the calf is left short, the precise effect on each individual calf is difficult to estimate (even though an average effect of rearing practice is known).
And in any case, there is variation in the quantity of milk produced by the dams. Selection among calves for growth rate therefore would be less accurate than in a totally uniform rearing system. A third problem is the opportunistic nature of the disposal of surplus stock that frequently occurs. The lack of a regular marketing strategy for well-grown animals, combined with the relatively rudimentary nature of the current marketing system, particularly in the remote areas, works against selection for “meat”.
Nonetheless, in the regions where yak products are in great demand in the marketplace, it seems that herdsmen have acquired both the knowledge and skill to improve production traits – even though it may be done unsystematically and perhaps unconsciously.
This is a possible reason why some breeds are held in higher esteem than others. But different breeds are rarely compared with each other in the same place and at the same time. So it is difficult to quantify the extent of any genetic differences in performance of the breeds, as distinct from differences in their looks.
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