Differences in body condition of gilts that are maintained from mating to the end of gestation affect mammary development

The goal of this project was to determine if different body conditions in late gestation that are due to varying body conditions at mating affect mammary development and mammary gene expression of gilts. Gilts that were fed ad libitum in the growing period were selected based on their backfat depths to form 3 groups at mating, namely, low backfat (LBF; 12–15 mm; n = 14), medium backfat (MBF; 17–19 mm; n = 15), and high backfat (HBF; 22–26 mm; n = 16). During gestation, LBF, MBF, and HBF gilts were fed approximately 1.25, 1.43, and 1.63 times maintenance requirements to maintain their differences in body condition. Feed intake was increased by 1 kg in the last 10 d of gestation. Backfat depths of gilts were ultrasonically measured at mating and on d 30, 50, 70, 100, and 109 of gestation. Blood samples were obtained at mating and on d 109 of gestation to measure concentrations of IGF-1, glucose, insulin, estradiol, urea, free fatty acids, leptin, and adiponectin. Gilts were slaughtered on d 110 of gestation to collect mammary glands for compositional analyses. Mammary extraparenchymal tissue weight was lesser in LBF and MBF gilts than in HBF gilts (1,259.3, 1,402.7, and 1,951.5 ± 70.4 g, respectively; P < 0.01). The weight of parenchymal tissue was not affected by treatment (P > 0.10), but its composition was altered. Concentrations of DNA and RNA decreased as backfat depth increased (P < 0.05), whereas percent fat and DM increased (P < 0.05). Circulating concentrations of leptin tended to be lower at mating (P < 0.10) and were lower on d 109 of gestation (P < 0.05) in LBF gilts than in HBF gilts. On d 109 of gestation, concentrations of insulin (P < 0.01) and IGF-1 (P < 0.05) were lower in LBF and MBF gilts than in HBF gilts, whereas those of urea were greater (P < 0.05). The mRNA abundance in parenchymal tissue for all genes studied was not affected by treatments (P > 0.10) with the exception of CSN2, which had a greater expression level in LBF gilts than in MFB or HBF gilts (P < 0.05). Percent of Ki-67–positive cells, used to assess mammary cell proliferation rate, was greater in HBF gilts than in LBF gilts (P < 0.05). When differences in body conditions of gilts that were present at mating were maintained throughout gestation, it had an impact on mammary development. Extraparenchymal tissue mass was affected and, more importantly, composition of parenchymal tissue was altered, indicating a beneficial effect of gilts being in the thinner treatment groups at mating.