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Journal of Dairy Science Vol. 81 No. 6 1724-1734
© 1998 by American Dairy Science Association ®
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Application of a Mechanistic Model to Study Competitive Inhibition of Amino Acid Uptake by the Lactating Bovine Mammary Gland

J. A. Maas 1, J. France 2, J. Dijkstra 3, A. Bannink 4, and B. W. McBride 1

1 Department of Animal and Poultry Science, University of Guelph, ON, N1G 2W1, Canada
2 Institute of Grassland and Environmental Research, North Wyke, Okehampton, United Kingdom EX20 2SB
3 Department of Animal Nutrition, Wageningen Agricultural University, PO Box 338, 6700 AH Wageningen, The Netherlands
4 Institute for Animal Science and Health, PO Box 160, NL-8200 AD Lelystad, The Netherlands

A mathematical model is used to describe uptake by a countertransport system and subsequent flow of three amino acids (AA), Phe, Val, and Met, from arterial blood to milk protein in the mammary gland of a lactating cow. The model suggests that total uptake of all AA is higher than net uptake and that a large proportion of the incoming AA is released from the cell directly back to blood. The model is used to predict which of the three AA is limiting the rate of milk protein synthesis and the response to increased arterial concentration of the first-limiting AA. Simulations are performed to predict possible outcomes of several experimental protocols to AA infusion, which might be used to test in vivo the responsiveness of the bovine mammary gland to an altered arterial concentration of AA. Of the three AA considered, arterial Met concentration appears to be first-limiting. The infusion profile that gives the greatest response in milk protein synthesis rate alters the arterial profile of AA such that it is identical to that of proteins originating in the mammary gland. Model construction can be simplified by acknowledging normal biological constraints.

Key Words: amino acid • transport • uptake • inhibition

Submitted on April 21, 1997
Accepted on January 7, 1998




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S. Noftsger and N. R. St-Pierre
Supplementation of Methionine and Selection of Highly Digestible Rumen Undegradable Protein to Improve Nitrogen Efficiency for Milk Production
J Dairy Sci, March 1, 2003; 86(3): 958 - 969.
[Abstract] [Full Text] [PDF]


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Copyright © 1998 by the American Dairy Science Association ®.