Prolactin (PRL), Prolactin Receptor (PRLR-LF) and Adiponutrin (PNPLA3) mRNA Abundances in Mammary Extraparenchymal Tissue of Gilts Are Affected By Body Condition

Study objectives were (1) to determine if different body conditions in late gestation, which were maintained from mating to day 110 of gestation, affect the mRNA abundance of adipokines and their receptors in mammary extraparenchymal tissue and (2) to look for associations between mammary gland composition variables and the gene expression of selected adipokines in extraparenchymal tissue. A total of 45 gilts were selected at mating according to their backfat thickness: low (LBF, 12-15 mm; n = 14), medium (MBF, 17-19 mm, n = 15) and high (HBF, 22-26 mm; n = 16) backfat. Throughout the gestation period LBF, MBF and HBF gilts received different amounts of a conventional diet to maintain similar backfat thicknesses from mating until the end of gestation. Gilts were slaughtered on d 110 of gestation. One side of the udder was dissected to evaluate mammary gland composition. Extraparenchymal tissue (mammary fat) was collected from the fourth teat of the other side to measure mRNA abundance of adipokines (ADIPOQ, LEP, PNPLA3, PRL) and their receptors (ADIPOR1, ADIPOR2, LEPR-LF, PRLR-LF) using real time-PCR amplifications. Statistical analyses were performed with the mixed procedure of SAS using a univariate model (3 levels) and means were compared with a Tukey test. The PROC CORR procedure of SAS was used for correlation analyses. In the extraparenchymal tissue, there was a greater PRL mRNA abundance in HBF than in LBF and MBF gilts (P<0.05). The PNPLA3 mRNA abundance was lower for HBF than MBF gilts (P<0.05), and lower PRLR-LF mRNA abundance was found in LBF than in HBF gilts (P<0.05). In the overall gilt population there was a negative correlation between the PNPLA3 mRNA abundance in extraparenchymal tissue and the percentage of parenchymal tissue fat (r = -0.30, P<0.05), and a positive correlation with the percentage of protein (r = 0.32, P<0.05). The PRL mRNA abundance in the extraparenchyma positively correlated with percent parenchymal dry matter (r = 0.42, P<0.01) and percent fat (r = 0.37, P<0.05). A negative correlation was observed between PRL mRNA abundance and the percent protein in parenchymal tissue (r = -0.31, P<0.05). Maintaining different backfat thicknesses from mating to the end of gestation affected PNPLA3, PRL and PRLR-LF gene expression in mammary extraparenchymal tissue. Correlation analyses show a relationship between PNPAL3 and PRL gene expression in extraparenchymal tissue and mammary gland composition at the end of gestation.