Amino acid uptake by the mammary gland of the lactating ewe

Davis, S.R.; Bickerstaffe, R.; Hart, D.S.

Australian Journal of Biological Sciences 31(2): 123-132


ISSN/ISBN: 0004-9417
PMID: 678219
Accession: 000286996

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The arteriovenous difference technique was used to measure amino acid uptake by the mammary gland of the lactating Merino ewe, which possesses a single large superficial epigastric vein. A method was developed enabling hourly measurement of milk yield without causing undue stress. Milk yield was essentially constant over a 7-8-h period. Mammary extraction of most non-essential amino acids was low relative to output in milk protein and showed a greater variability with time than that found for the essential amino acids. There was a significant mammary extraction of ornithine and citrulline, neither amino acid being found in ovine milk protein. Of the essential amino acids, valine, isoleucine, leucine and arginine were taken up in excess of their requirement for milk protein synthesis. On the basis of the extent of mammary extraction, methionine, lysine and leucine were 1st, 2nd, 3rd-limiting to the rate of milk protein synthesis. Despite fluctuations in arterial amino acid concn. the arteriovenous differences of the essential amino acids were relatively constant over a 7-8-h period. The pattern of mammary amino acid uptake in the ewe is contrasted with that found in similar studies carried out with the lactating cow and goat.