Determining the Role of Energy on Mammary Gland Utilization of Plasma Amino Acid

Abstract

Our overall objective is to investigate nutritional strategies that upregulate signaling pathways of milk protein synthesis directing nitrogen towards milk production, therefore reducing the amount of nitrogen waste entering the environment. Targeting the mTORC1 pathway shows promise as it coordinates nutrient and environmental cues to stimulate cellular anabolic processes, like protein and fat synthesis. Previously, our lab has demonstrated that insulin and amino acids (AA) synergistically stimulate mammary mTORC1 activity. We hypothesized that glucogenic energy, by stimulating insulin secretion and potentiating AA activation of mammary mTORC1 activity, would increase sequestration of AA for milk protein synthesis. To test our hypothesis, 36 peak-lactation Holstein cows were used in a 4x4 repeated Latin square design with four 28-d periods and four treatments arranged as a 2x2 factorial. The two treatment factors were energy source: glucogenic (GE) or ketogenic (KE) and total metabolizable AA: 10% deficient (DAA) or sufficient (BAA). Blood samples from a subset of 20 cows were collected from coccygeal vessel (artery) and subcutaneous abdominal (mammary) vein 6 timepoints during the last 2 days of each period. Plasma was isolated by centrifugation and mixed with isotopically labeled AA as internal standards for AA analysis by liquid chromatography-mass spectrometry. Mammary blood flow was calculated based on the Fick principle, using Phe+Tyr as non-metabolizable markers. Plasma concentrations, mammary extraction efficiency and uptake were calculated, and statistical analysis was applied. Plasma amino acid concentration, extraction and uptake were significantly affected by energy source and AA level, with few treatment interactions. Although the ketogenic diet had an increased response in milk protein g/d (P¬ = 0.03), overall increased sequestration of amino acids was not observed, with only significant increases in Arg (P¬ = 0.01) and Ser (P¬ = 0.02) mammary uptake.