A hyperinsulinemic-euglycemic clamp was used to investigate the effect of insulin on milk protein synthesis in wellfed Holstein cows (n=4) with or without additional amino acids. Cows were fed a dry total mixed ration diet formulated to exceed requirements for metabolizable energy and protein. During abomasal water infusion, the insulin clamp increased milk protein yields by 15% (+128 g/d; P<0.01); when combined with abomasal infusion of casein plus branched-chain amino acids, milk protein yield was increased by 25% (+213 g/d; P<0.01). Concentrations of casein and whey proteins in milk were increased by insulin clamp treatments, with little change in their relative proportions. Providing amino acids without the insulin clamp had no effect on any production variables. Results confirm the important regulatory role of the endocrine system in milk protein synthesis and demonstrate the potential to produce milk protein is not fully expressed.
Proceedings of the New Zealand Society of Animal Production, Volume 60, Hamilton, 303-306, 2000
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