Peripartal endocrine changes and the initiation of lactation in ewes of diverse breeds

Perinatal endocrine changes and associated patterns of various milk constituents were examined in multiparous ewes from diverse breeds. Maternal progesterone, estrone, estradiol-17 beta, cortisol and prolactin patterns were measured simultaneously during the peripartal period in Dorset, Rambouillet (Ra) and Finnish Landrance (Finn) ewes, with characteristic gestational durations of 146.0 +/- 0.91, 148.4 +/- 1.05 and 144.8 +/- 0.67 days, respectively. Changes in milk lactose, protein, fat and energy content were also examined in the subsequent lactation periods. Significant (P less than 0.05) declines in progesterone, with progressive increases in estradiol and estrone preceded an abrupt elevation in prolactin levels in all breeds near term. Consistent increases in maternal cortisol levels were noted immediately prior to parturition in all ewes and remained elevated for a few days in the first week of lactation, although other endocrine parameters had declined significantly. Similar peripartal endocrine changes in all ewes, corresponded to significant (P less than 0.05) increases in milk lactose, protein and fat content during the first 3 days of lactation. Milk lactose in particular was closely associated with low progesterone concentrations and a return of postpartal prolactin levels to prepartal concentrations. The initiation of lactation and subsequent composition of ewes' milk were not markedly affected by chronological changes in endocrine patterns, characteristic to diverse breeds with varying gestational durations.