Development of mammary glands of fat sheep submitted to restricted feeding during late pregnancy

Mammary gland development in sheep occurs mainly during puberty and pregnancy. We have investigated the effects of a late gestation feed restriction on mammary gland development in sheep. Five control ewes were slaughtered d -38 from parturition, whereas 10 ewes were fed ad libitum and another 10 ewes were fed restrictedly (50% of energy and protein requirements) the last 38 days of pregnancy. Half the ewes in each feeding treatment group were slaughtered d -6 from parturition. Both mammary glands were collected at slaughter. From the remaining five sheep in each feeding group, blood and mammary biopsies were collected on d - 16, d -6, d 5 and d 30 from parturition. Fetus weights, weight of mammary parenchyma, amount of mammary epithelium and rate of mammary cell proliferation increased from d -38 to d -6 from parturition, but was not significantly affected by late gestation feed restriction. Colostrum yield was reduced (P = 0.02) by feed restriction, but milk yield at d 5 and d 30 was not (P = 0.12). Mammary gene expressions of alpha-lactalbumin (P = 0.97), leptin (P = 0.36), Bcl-2 (P = 0.35), Bax (P = 0.21), insulin-like growth factor 1 (IGF-I) (P = 0.81) and cyclin D1 (P = 0.43) were not affected by feed restriction, although plasma IGF-I (P = 0.13) and leptin (P = 0.04) concentrations were reduced by feed restriction. Our results suggest that extensive mobilization of body tissues occurred during late gestation feed restriction, which compensated for the reduced dietary nutrient supply, thereby maintaining fetal and mammary gland development, and this was likely explained by a high initial level of body fat in the experimental ewes. The colostrum yield was impaired by feed restriction, but our results show that in multiparous sheep, adequate post-partum nutrition can support lactational performance. In conclusion, mammary redevelopment in between successive lactations is not significantly affected by feed restriction during late pregnancy in fat sheep. (C) 2007 Elsevier B.V. All rights reserved.