Effect of litter size (birth type) on milk yield and composition in goats and sheep production

Abstract

Litter size is one of the major external (non-genetic) factors which has a multifaceted influence as it regulates both reproduction and production in goats and sheep. Apart from being a principal source of variation on kid/lamb growth performance and survivability, litter size has been implicated in influencing milk yield and composition. However, it is important to note that the influence of litter size on milk constituencies such as protein, fat, lactose, pH, colostrum, etc. has been inconsistent in a number of studies. In absolute terms, milk production is a function of animal genetics and an array of non-genetic factors, and among the latter litter size is ranked highly. There is a tendency of prolificacy promoting high milk production, which implies multiple birth will enhance milk production. The positive relationship between litter size and milk production with regards to multiple bearing dams outperforming single bearing dams is due to prolactin stimulation of the udder which depends on the intensity of the suckling stimulus in response to the number of kids/lambs in a litter. It is more likely that the relationship between milk yield and litter size is for the most part dependent on the extent of prepartum development of the mammary gland where prolactin plays a major role. There is a distinct and strong established physiological link between the number of foetuses in a dam, the resultant placental mass and lactogenic (hormonal) function of plasma to advancement and development of mammary gland in the course of pregnancy and of litter size to milk production. The underlying drivers of milk production are developed in a way specified during fertilization and embryogenesis’s based on the development of placental mass which has a hormonal influence on mammary development in turn milk production. Larger litters promote extensive formation of placental mass as compared with small sized litter. The greater the placental mass as a function of larger litter size the greater the extent of mammary growth hence the greater the dams’ milking capacity. The relationship between litter size and milk composition has been inconclusive as indicated by inconsistency of study results by various authors. The present discussion explores the significance of litter size (birth type) on milk yield and composition in goats and sheep production.