Differences in body condition of gilts that are maintained from mating to the end of gestation affect their 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 of gilts. Gilts that were fed ad libitum in the growing period were selected based on their backfat thickness (BF) to form three groups at mating, namely, low (LBF; 12-15 mm, n = 14), medium (MBF; 17-19 mm, n = 15), and high (HBF; 22-26 mm, n = 15) BF. During gestation, LBF, MBF, and HBF gilts were fed approximately 1.25, 1.43 and 1.63 of maintenance requirements to maintain their differences in body condition. Daily feed intake was increased by 1 kg in the last 10 d of gestation. All gilts had their BF measured ultrasonically at mating and every 15 to 20 d thereafter. Blood samples were obtained at mating and on d 109 of gestation to measure concentrations of IGF-1, glucose, insulin, estradiol, urea, FFA and adiponectin. Gilts were slaughtered on d 110 of gestation to collect mammary glands for compositional analyses and measures of mRNA abundance for selected genes. The MIXED procedure of SAS using a univariate model (3 levels) was used for statistical analyses and means were compared using the Tukey’s test. Mammary extraparenchymal tissue weight was lesser in LBF and MBF than in HBF gilts (1259.3, 1402.7 and 1951.5 ± 70.4 g, respectively, P < 0.01). Weight of parenchymal tissue was not altered by treatment (P > 0.10), but its composition was affected. Concentrations of DNA and RNA decreased as BF increased (P < 0.01), whereas percent fat and dry matter increased (P < 0.01). Mammary expression of CSN2 (β-casein) in parenchymal tissue was also lower in HBF than LBF gilts (P < 0.05). On d 109 of gestation, concentrations of insulin, IGF-1 and adiponectin were greater (P < 0.05) in HBF than in LBF or MBF gilts, whereas those of urea were lower (P < 0.01). Maintaining differences in body condition from mating to the end of gestation therefore had an impact on mammary development of gilts. Extraparenchymal tissue mass was affected and, more importantly, composition of parenchymal tissue.