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EFFECTS OF DIETARY CARBOHYDRATE AND PROTEIN ON MAMMARY NUTRIENT UTILIZATION IN LACTATING DAIRY COWS

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Title: EFFECTS OF DIETARY CARBOHYDRATE AND PROTEIN ON MAMMARY NUTRIENT UTILIZATION IN LACTATING DAIRY COWS
Author: Curtis, Richelle V.
Department: Department of Animal Biosciences
Program: Animal and Poultry Science
Advisor: Cant, John P.
Abstract: The main objective of this thesis was to investigate effects of nutritional status, particularly of carbohydrate and protein, on lactational performance, mammary nutrient utilization and gene expression in dairy cows. The first experiment was conducted to characterize mammary transcriptional response to starch level on low- and high-protein diets in eight lactating dairy cows. Cows consuming the high-starch diets had greater milk protein yields (MPY) and greater expression of a translational machinery-related gene, indicating that starch stimulates MPY through increases in translational capacity in mammary secretory cells. The objective of the second experiment was to investigate mammary utilization of blood metabolites, as well as further characterize mammary and muscle gene expression in twelve lactating dairy cows receiving infusions of glucose and two levels of branched-chain amino acids (BCAA) consuming a low-protein diet. Glucose infusions increased milk and MPY, reduced total and BCAA plasma concentrations but did not affect mammary uptakes of amino acids. Provision of BCAA caused reduced MPY, decreased circulating non-branched-chain essential amino acids, as well as mammary uptake, and did not affect plasma urea concentrations. Results indicate that the glucose effect on MPY was not limited by low BCAA concentrations, and that stimulation of non-mammary peripheral tissue use of non-branched-chain essential amino acids by BCAA led to a decrease in MPY. Finally, mammary gene expression was found to be unaffected by infusions or dietary protein and although select expression of genes in the muscle were affected, it was difficult to make any definitive conclusions. The research conducted here in this dissertation has shown that low plasma BCAA are not responsible for the poor stimulation of MPY in response to glucose. Furthermore, it has demonstrated that elevated plasma BCAA concentrations appear to stimulate protein synthesis in non-mammary peripheral tissues rather than in the mammary glands of lactating dairy cows.
URI: http://hdl.handle.net/10214/12173
Date: 2018-01-11


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