Dietary restriction during gestation and mother-calf bond in sheep

a review

Abstract

The aim of this review was to summarize and to discuss the available information about the effects of subnutrition during gestation on ewe-lamb bond at lambing and during lactation period. The bond between the ewe and the lamb, that is highly selective, is established immediately after lambing through olfactory, auditory and visual signals. Immediately after lambing, if the ewe accepts the lamb, it allows it to suckle colostrum; however, if it does not accept it, she rejects it with aggressive behaviours. During the lactation period, the maternal care changes until the total independence of the lamb, ending in natural weaning. However, in most productive systems, lambs are separated from the dams at an earlier age, provoking behavioural and physiological responses indicative of stress in both, the ewe and the lamb. In Uruguay, sheep breeding systems that predominate are extensive, based on grazing native pastures, presenting a great decrease in forage availability in winter, when ewes are pregnant. Thus, pregnant ewes suffer a nutritional restriction, losing body weight, and consequently achieving lower birth weight and less body energetic reserves of their lambs, weakening the ewe-lamb bond. Failures in the establishment of mother-young bond are one of the main causes of the high neonatal mortality rates, and thus, the low reproductive efficiency achieved in these systems. Moreover, undernourished pregnant ewes produce less lactation period, and modifying the stress response at artificial weaning.