Effect of genetic and non-genetic factors on growth traits in goats and sheep production

Abstract

Birth weight, weaning weight and efficiency of pre and post weaning gains are growth traits of economic importance with regards to the cost and efficiency of meat production in goats and sheep. It is important to note that growth traits are not only influenced by environmental factors, but also genetic potential of individual kid/lamb. Nutrition is ranked highly among the environmental factors affecting growth traits, however, climate and seasonal differences among different years affect the production of the whole flock, while sex, type of birth, age and weight affect the individual growth performance. Birth size/weight represents the greatest initial barrier on weaning and pre-weaning growth among the non-genetic factors in both goats and sheep. Therefore, understanding of the extent of influence of both genetics and environmental factors becomes very important for devising efficient and effective management plans in goats and sheep. Kids/lambs born out of multiple birth might be at a disadvantage against singletons in terms of pre-weaning growth, individual weaning weight as they progress into post weaning growth. Differences in kid/lamb weaning and post weaning performance between years is an indicative of environmental variations (variation of quantity and quality of herbage available), which cannot be manipulated. One outstanding, and often reported feature of weaning weight is the tendency for it to be sex biased, where male kids and lambs are superior weaning weight as compared with female kids/lambs. In order to increase pre- and post-weaning growth performance as well as weaning weights in goats and sheep production, efforts must be directed at improving nutritional status, breeding and management of animals. The sort management strategy should take cognisance of the various factors that influence growth traits from birth through weaning and then post weaning growth which is predictive of weight at slaughter. The significant effect on pre-weaning and post-weaning growth found to be year of weaning, nutrition/age of dam, and sex of the kids/lamb have practical implications not only for the husbandry of the goats and sheep as an economical commodity, but also for the increased knowledge of factors that are determinants of variation in weaning performance and growth traits in goats and sheep. The present review gives an insight on some determinants of weaning weight, pre and post weaning growth in goats and sheep.