A review of the behavioural and physiological adaptations of hill and lowland breeds of sheep that favour lamb survival

Abstract

Extensively managed animals, often living in harsh and unfavourable environments, need specific adaptations that promote survivability. This is particularly important at parturition and during the neonatal period, when ewe and lamb mortality is highest. To understand the survival adaptations of extensively managed breeds, we reviewed the behavioural and physiological adaptations of ewes and lambs of hill (extensive) breeds of sheep to lowland (intensively managed) breeds during pregnancy, parturition and lactation. Hill sheep have a smaller average litter size than lowland sheep but carry a significantly heavier litter (proportional to their own body weight), which may be achieved through more efficient placental exchange. Isolation seeking at parturition by the ewe is affected by maternal experience and familiarity with the environment. However, an increase in domestication and intensification appear to have led to a decrease in isolation seeking at parturition. Hill ewes have a shorter labour, and an easier delivery than lowland ewes, which may be partly related to pelvis dimensions and to lamb characteristics. Hill ewe breeds lick their newborn lambs more than lowland ewes immediately after birth, and have a higher rate of low-pitched bleating (both important behaviours for the development of ewe–lamb attachment). These behavioural differences result in better ewe–lamb recognition 24 h after birth in hill ewes, and closer ewe–lamb spatial relationships during lactation. Hill ewes are more aware of the presence of their lambs during lactation, which may aid defence of the lamb against predators. Hill lambs are quicker to stand and suck after birth than lowland lambs, and show better maternal recognition than lowland lambs. Hill lambs also maintain higher rectal temperatures after birth than lowland lambs and have better cold resistance. Better thermoregulation is partly related to birthcoat characteristics, but is also accompanied by higher thyroid hormone concentrations (important for endogenous heat production) in hill than lowland lambs. The colostrum of hill ewes has higher lipid content than lowland ewes, which may also contribute to improved thermoregulation. This suggests that hill sheep, adapted to extensive management systems, have evolved more efficient behavioural and physiological mechanisms to enhance lamb survivability in harsh environments than have intensively managed lowland sheep breeds.