130 Parity affects mammary development in late-pregnant swine

Abstract

Abstract This project was undertaken to determine if mammary development at the end of gestation differs between primiparous and multiparous sows. During gestation, primiparous (n = 19) and multiparous (parities 2 and 3, n = 17) Yorkshire × Landrace sows were fed one daily meal of a conventional corn-based diet. Amounts fed were based on body weight (BW) and backfat thickness at mating. On d 110 ± 1 of gestation, a jugular blood sample was obtained from all sows to measure IGF-1, glucose, FFA and urea. Sows were then weighed and their backfat thickness measured before euthanasia. Mammary glands from one side of the udder (7 glands) were dissected for compositional analyses. The fifth gland of the contralateral row of mammary gland was sampled for histology and immunohistochemical localization of Ki67. There was less total parenchyma (1,437.4 vs 2,004.7 ± 127.1 g) and total extra-parenchymal tissue (1,691.0 vs 2,407.0 ± 125.3 g; P < 0.001) in mammary gland of primiparous compared with multiparous sows. When these values were expressed per kg BW (respective means of 226.0 and 284.0 ± 2.7 kg for primiparous and multiparous sows), there was no difference for either parenchyma or extra-parenchymal tissue across parity groups (P > 0.05). Parity altered all components within the parenchyma (P < 0.001). Specifically, parenchymal tissue from primiparous sows had greater fat and DM percentages, decreased protein percent, and reduced concentrations of DNA (6.59 vs 9.35 ± 0.53 mg/g DM) and RNA (7.76 vs 12.33 ± 0.70 mg/g DM) than that from multiparous sows. On the other hand, the circumference of alveolar lumens was greater in primiparous than multiparous sows (P < 0.001), and the percentage of epithelial cells that were positive for Ki67, an indicator of cell proliferation, also tended to be greater in primiparous sows (P = 0.07). Circulating concentrations of IGF-1 were greater in primiparous than multiparous sows (45.0 vs 27.3 ± 2.8 ng/mL, P < 0.001). None of the other blood variables were affected by parity (P > 0.10). Results show a marked effect of parity on mammary gland development in swine. At the end of gestation, primiparous sows had less developed mammary parenchyma with a tendency for a greater rate of proliferation than multiparous sows. Such a difference could affect the response of mammary tissue to various nutritional or endocrine signals. This information is crucial for developing optimal management strategies that will maximize sow milk yield.