Endocrinology and mammary development of lactating Genex-Meishan and Large White sows

Farmer, C., Palin, M. F. and Sorensen, M. T. 2003. Endocrinology and mammary development of lactating Genex-Meishan and Large White sows. Can. J. Anim. Sci. 83: 731-737. Endocrine and metabolic data as well as mammary tissue composition were obtained in Genex-Meishan (GM, containing 50% Chinese Meishan genes) and Large White (LW) lactating sows. Jugular vein cannulae were used to collect serial blood samples from 9 LW and 8 GM sows for 4 h every 15 min on days 6 and 19 of lactation. Concentrations of prolactin and cortisol were determined on all samples while those of insulin-like growth factor-I (IGF1), growth hormone (GH), glucose and free fatty acids (FFA) were measured in hourly samples. Milk samples were obtained from 19 GM and 16 LWsows on day 23 of lactation and all sows were slaughtered on day 25. Mammary glands were excised and analyzed for tissue composition and for number and affinity of prolactin receptors. Concentrations of plasma IGF-I were lower (P < 0.01) and plasma FFA greater (P < 0.001) in GM than in LW sows. On day 6 of lactation, serum prolactin (P < 0.05) and cortisol (P < 0.01) concentrations were greater and glucose values lower (P < 0.001) in GM than in LW sows. The concentration of IGF1 in lactoserum was lower (P < 0.001) while that of prolactin was greater (P < 0.05) in GM compared to LW sows on day 23 of lactation. There was less (P < 0.001) residual milk and more (P < 0.05) parenchymal RNA in mammary glands from GM compared to LW sows. The affinity of prolactin receptors was also greater (P < 0.05) in GM than in LW sows. The better emptying of mammary glands by litters from GM sows and the greater circulating concentrations of prolactin in early lactation as well as the greater affinity of mammary prolactin receptors may be related to the great milking potential of Meishan-derived sows.