Mammary gland development and hormone levels in pregnant Upton-Meishan and large white gilts.

Genetic differences between Upton-Meishan (UM, n = 13) and Large White (LW, n = 14) gilts were studied with regard to mammary gland development and concentrations of hormones. Gilts were weighed and their backfat measured at mating, and at d 70 and 109 of gestation. Jugular blood samples were also collected at these times and assayed for prolactin, cortisol, IGF-I, insulin, glucose, progesterone, and estradiol. Gilts were slaughtered on d 110 of gestation. One row of mammary glands was used for dissection and biochemical analyses. The other row was used for determination of prolactin receptor number and affinity. UM gilts weighed less (P<0.05) and had more backfat (P<0.01) than LW gilts at all times. Parenchymal tissue weight was less (P<0.05) in UM gilts. Percent fat (P<0.001) and dry matter (P<0.001) in parenchymal tissue were greater in UM gilts while that of protein (P<0.001) was lower. Total protein weight in parenchyma was also lower in parenchyma was also lower in UM gilts (P = 0.01). Both DNA (P<0.001) and RNA (P<0.001) contents were lower in UM gilts while RNA/DNA remained similar (P>0.1). Number of prolactin receptors were lower (P = 0.06) and affinity greater (P<0.05) in UM gilts. Cortisol levels were greater (P<0.01) in UM gilts while other hormones were not affected (P> 0.1). Results clearly demonstrate genetic differences with regard to mammogenesis in gilts and suggest that the less mammary gland development in Upton-Meishan compared with Large White breed of gilts may be related to lower number of prolactin receptors.