Dam breed effect and other dam related non-genetic factors as determinants of growth traits in goats and sheep production
Ewes/does individual performance is a prime factor that influence the overall meat productivity and profitability in goat and sheep production. The number of kids/lambs born per ewe/doe per year, effectively weaned and marketed at a desirable weight are absolutely essential components for the viability of any commercial goat and sheep enterprise. Hence one principal source of substantial meat production inefficiency in commercial goat and sheep production is poor maternal effects which compromise high kid/lamb growth, where a larger proportion of kid/lamb crop fails to attain desirable marketable weight resulting in immense economic losses. There is apparent evidence accrued through extensive studies in goats and sheep which point to the fact that heredity of the dam and other dam related non-genetic factors such as parity order, dam nutrition, age and weight of dam at kidding/lambing and the dam’s body condition score influence kid/lamb pre-weaning growth trait and the actual weight at weaning. In this respect, birth weight, pre and post weaning weight gain of kids/lambs may vary with dams’ genotype, parity, dams’ nutrition, litter size as a dams’ trait, dam weight/age and parity order. The resultant effect of genotype of dam on kid/lamb growth can be direct or indirect, firstly there is a direct contribution of half of the dams’ genes to the progeny for potential growth of kids/lambs, and secondly the indirect effect comes from dam possessing genes for milk production enough to adequately nurse their kids/lambs hence promoting desirable growth. It is important to note that dam milking capacity is dependent on breed, in addition to being influenced by other environmental factors such as dam nutrition and parity order. Kid/lamb born to high milk producing dams are highly likely to outclass their counterparts in post weaning growth weight gain, as well as the actual weaning weight. Low birth weight kid/lamb are associated with poor nutrition of dams during pregnancy and its effects could be seriously felt in multiple birth which result in compromised post weaning growth. Genetics is a primary source of variation for prolificacy in goats and sheep hence litter size can be designated as a maternal trait. The higher the size of birth the lower the weaning weight because of nursing competition due to multiple birth in large litter size. Mature dams give birth to heavier kids and provide enough milk to nursed kids/lambs promoting faster growth rates subsequently enhancing survivability of kids/lambs. There is potentiality of manipulation of husbandry practices focusing on ensuring that all born kids/lambs are as close as possible to the acceptable birth weight average for that specific breed of choice which can sustain desirable weaning and post weaning growth. It should be noted that due to multifaceted nature of the dam determinants of growth traits it is reasonable to assume that appreciation of specific cause and occurrence of kids’/lamb growth could be advantageous to minimize retarded growth rates. A total control of kid/lamb growth is probably unachievable as a result partly targeting the control of both environmental and dam-related factors is critical. High kid/lamb growth rates necessitate for good management practices and improved dam nutrition to support nursing of multiple birth, in addition to the exploitation of crossbred’s heterosis to promote growth in kids/lambs. The present review gives an insight on the influence of dam related factors on pre and post-weaning growth, as well as actual weaning weight in goat and sheep production.
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