Body condition of gilts at the end of gestation affects their mammary development

The impact of body condition at 110 d of gestation on mammary gland development, mammary gene expression, and hormonal and metabolite status of gilts was studied. Thirty-nine gilts were equally divided into 3 groups based on their backfat thickness at the end of gestation: 1) low backfat (LBF; 12–15 mm), 2) medium backfat (MBF; 17–19 mm), or 3) high backfat (HBF; 21–26 mm). Gilts had similar BW (138.1 ± 8.2 kg) and backfat thicknesses (16.4 ± 1.0 mm) at mating and the 3 groups were achieved via ingestion of varying amounts of feed throughout gestation. Jugular blood samples were obtained from all gilts at mating and at 109 d of gestation to assess hormonal and metabolic statuses, and animals were slaughtered on d 110 to collect mammary glands for compositional analyses and for measure of gene expression. The LBF gilts had less extraparenchymal tissue (P < 0.01) and parenchymal tissue (P < 0.05) than HBF gilts. Mammary parenchyma from LBF gilts also tended to contain less DM (P < 0.10), contained more protein (P < 0.05), and had greater RNA concentrations (P < 0.01) than that from HBF gilts. None of the 15 genes studied in mammary parenchymal tissue differed in terms of expression level, and the rate of mammary cell proliferation was similar among treatments (P > 0.10). There was a tendency for circulating leptin concentrations on d 109 of gestation to be lower in LBF gilts than in MBF gilts (P < 0.10), whereas values for HBF gilts did not differ from those of the other treatments (P > 0.10). Current results demonstrate that being too thin at the end of gestation (12–15 mm backfat) has a negative impact on mammary development in gilts, whereas having backfats varying from 17 to 26 mm seems to have no detrimental effects on mammogenesis. Backfat thickness in late pregnancy must therefore be considered to achieve optimal sow lactation performance.