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J. Dairy Sci. 2009. 92:130-138. doi:10.3168/jds.2008-1450
© 2009 American Dairy Science Association ®
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Effects of glucagon infusions on protein and amino acid composition of milk from dairy cows1

G. Bobe2, A. R. Hippen, P. She, G. L. Lindberg, J. W. Young and D. C. Beitz3

Nutritional Physiology Group, Department of Animal Science, Iowa State University, Ames 50011

3 Corresponding author: dcbeitz{at}iastate.edu

Changing the composition of milk proteins and AA affects the nutritional and physical properties of dairy products. Intravenous infusions of glucagon decreases milk protein production and concentration by promoting the use of gluconeogenic blood AA for hepatic glucose synthesis. Little is known about how the diversion of AA to gluconeogenesis affects the composition of milk proteins and AA. The objective was to quantify changes in composition of milk protein and AA in response to i.v. glucagon infusions. Three separate experiments were used: 1) 8 Holstein cows were fed ad libitum and infused with glucagon at 10 mg/d for 14 d, 2) 7 Holstein cows were feed restricted and infused with glucagon at 10 mg/d for 14 d, and 3) 4 Brown Swiss cows were infused with glucagon at 5 and 10 mg/d for 2 d each. Milk and milk component yields and milk protein and amino acid composition of samples, collected with blood samples at the first and last day of the glucagon infusion period, were compared with those collected 1 d before and after the glucagon infusion period. Glucagon infusions decreased milk protein production and concentration in each experiment by at least 0.2 ± 0.05 kg/d and 4 ± 0.4 g/L, respectively. The decrease was accompanied by changes in milk protein composition, the most consistent being an increase in {kappa}-casein (1.68 ± 0.27%). Overall, glucagon infusions resulted in higher proportions of {kappa}-casein and {alpha}S2-casein (1.34 ± 0.51%) and smaller proportions of {alpha}S1-casein (–3.83 ± 1.75%) and {alpha}-lactalbumin (–0.91 ± 0.32%). Glucagon had little impact on milk AA composition except an increase in glycine (0.26 ± 0.11%). The results suggest that milk protein synthesis is regulated by many factors including AA and glucose availability.

Key Words: dairy cow • glucagon • milk protein composition • milk amino acid composition




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G. Bobe, G. L. Lindberg, L. F. Reutzel, and M. D. Hanigan
Effects of lipid supplementation on the yield and composition of milk from cows with different {beta}-lactoglobulin phenotypes
J Dairy Sci, January 1, 2009; 92(1): 197 - 203.
[Abstract] [Full Text] [PDF]


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