Genetic and physiological determinants of maternal behavior and lamb survival: implications for low input sheep management

¹ Sustainable Livestock Systems Group, SAC, Edinburgh, EH9 3JG, UK

^* To whom correspondence should be addressed. E-mail: cathy.dwyer{at}sac.ac.uk.

	Abstract

The relatively intensive supervision afforded many ewes at lambing time is a barrier to the development of low-input sheep management systems. However, in some flocks, reduction in this level of supervision may, initially, affect lamb mortality and animal welfare. In this review, possibilities for optimizing behavioral interaction between the ewe and lamb, with the goal of improving lamb survival without the need for high levels of human supervision, are considered. At birth, ewes show specific behavioral patterns (e.g., licking or grooming, low-pitched bleats, udder acceptance) that facilitate the transition of the lamb from pre to postnatal life, and accompany the formation of an exclusive, olfactory memory for the lamb. The lamb also performs a specific sequence of behaviors directed towards standing, finding the udder and sucking. The successful accomplishment of these behavior patterns is vital for a strong attachment to be formed between both partners, and for lamb survival. The expression of maternal behavior in the ewe is affected by her previous maternal experience, by nutrition in pregnancy, by breed, by temperament and, to some extent, by the behavior of her lamb. The maternal care expressed by a ewe at parturition is indicative of her behavior throughout that lactation and successive pregnancies, suggesting an underlying basis to maternal care intrinsic to that ewe. Studies with Scottish Blackface and Suffolk ewes show that ewes expressing high levels of maternal care have elevated plasma estradiol in late gestation compared to ewes with poorer maternal care, and that circulating estradiol concentration is correlated with maternal behaviors. Although the genetic basis of maternal behaviors has still to be fully determined, there are possibilities to improve maternal behavior by selection and a better understanding of the neuroendocrine processes underlying individual differences in maternal behavior may help in developing selection strategies. In addition, selection on lamb behaviors, which show some genetic basis, may also be a route to improve lamb survival. Because both ewe and lamb behavior are affected by environmental factors, appropriate management, through pregnancy and at parturition, will enhance the expression of maternal behavior and lamb vigor, and so contribute to improving lamb survival.

Key Words: Estradiol, Genetics, Lamb survival, Management, Maternal behavior, Sheep