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Journal of Dairy Science Vol. 79 No. 8 1425-1429
© 1996 by American Dairy Science Association ®
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Responses in Milk Constituents to Intravascular Administration of Two Mixtures of Amino Acids to Dairy Cows

J. A. Metcalf 1, L. A. Crompton 1, D. Wray-Cahen 1, M. A. Lomax 1, J. D. Sutton 1, D. E. Beever 1, J. C. MacRae 2, B. J. Bequette 2, F. R. C. Backwell 2, and G. E. Lobley 2

1 University of Reading, Centre for Dairy Research, Hall Farm, Arborfield, Reading, England RG2 9HX
2 Rowett Research Institute, Greenburn Road, Bucksburn, Aberdeen, Scotland AB2 9SB

Four Holstein-Friesian cows were used to investigate the effects of intravascular infusions of AA mixtures on milk constituents. Cows were in wk 11 to 28 of lactation and were fed a basal concentrate (142 g of CP/kg of DM) and grass silage (149 g of CP/kg of DM) in a. 60:40 ratio (percentage of DM). Cows were fed hourly, and feed intake was fixed at 95% of ad libitum intake for each experimental period. Each cow received a 4-d jugular saline infusion, followed by a 5-d jugular infusion of a mixture of AA. Two mixtures of AA were used in a crossover design. The first mixture contained both the essential AA and non-essential AA found in milk protein (total AA); this mixture was infused at 400 g of AA/d. The other mixture represented the essential AA fraction only and was infused at 208 g/d. Infusion of total AA increased milk protein concentration from 32.4 to 35.0 g/kg, and essential AA increased milk protein concentration from 32.5 to 36.9 g/kg; milk protein yield increased by 87 g/d (total AA) and 143 g/d (essential AA). Intravascular administration of AA specifically stimulated milk protein concentration, and the efficiency with which the AA were used was higher than had been previously reported when AA supply was increased either by dietary supplementation or by abomasal infusion.

Key Words: amino acids • lactation • milk • protein

Submitted on June 12, 1995
Accepted on May 17, 1996




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