Nutritional and Regulatory Roles for Branched-Chain Amino Acids in Milk Production by Lactating Sows

Abstract

Both feeding and cell culture studies were conducted to test the hypothesis that branched-chain amino acids (BCAA) can enhance milk synthesis by porcine mammary epithelial cells (PMEC). In the first in vivo feeding trial, ten multiparous lactating sows were fed corn-soybean meal-based diets supplemented with 0%, 1.535%, or 3.07% BCAA for 29 d. The number of piglets was standardized to 9 per sow. On d 3,15 and 29 of lactation, body weights of sows and their piglets, as well as milk consumption of piglets were determined. Blood samples were obtained from sows and piglets at 2 and 1 h after feeding, respectively. The second feeding experiment was conducted with dietary supplements containing 0%, 1% or 2% monosodium glutamate (MSG). Data were analyzed by two-way ANOVA. In both feeding trials, plasma concentrations of aspartate, glutamine, citrulline, arginine, and BCAA were higher, compared to the control. Dietary supplementation with 1.535% and 3.07% BCAA increased: 1) concentrations of free and protein-bound glutamate plus glutamine in milk; 2) milk intake of piglets by 14% and 21%; and 3) daily weight gains of piglets by 19% and 28%. Dietary supplementation with 1% and 2% MSG increased: 1) concentrations of free and protein-bound glutamate plus glutamine in milk; 2) milk intake of piglets by 14% and 25%; and 3) daily weight gains of piglets by 23% and 44%. These results indicated that dietary supplementation with up to 3.07% BCAA or 2% MSG was safe and enhanced lactation in sows. To elucidate the mechanisms responsible for the effects of BCAA on milk production, PMEC were cultured in customized medium containing 0.1, 0.25, 0.5, 1 or 2 mM L- leucine, L-isoleucine, or L-valine, or a mixture of those three BCAA. Elevating extracellular concentrations of BCAA from 0.1 to 2 mM increased the phosphorylation of proteins in the mechanistic target of rapamycin pathway, the rate of protein synthesis and cell proliferation, while decreasing the abundance of proteasome and ubiquitinated protein, and the rate of protein degradation in PMEC. The findings not only advance understanding of nutritional regulation of lactation but also provide a new strategy to improve milk production by livestock, women, and other mammals.