Mammary Blood Flow and Regulation of Substrate Supply for Milk Synthesis

S. R. Davis, R. J. Collier

Research output: Contribution to journalArticle

94 Scopus citations

Abstract

In ruminants, mammary supply of substrate varies with rate of mammary blood flow and concentrations of blood substrates. Blood concentrations of most mammary substrates, except acetate and tryptophan, do not vary greatly with feed intake, short term. Fasting reduces mammary blood flow, whereas milking and injection of growth hormone or thyroxine increase flow. It is proposed that the fraction of cardiac output that perfuses the udder of lactating ruminants plays a role in regulation of nutrient partitioning between milk and body tissues. In fed animals this fraction is 15 to 16% of cardiac output, which declines on fasting to 8 to 9% and increases slightly following growth hormone treatment to 17.6%. Following realimentation of fasted cows or goats, mammary blood flow takes several hours to return to normal. Investigation of the mechanism of this response, in terms of the ability of the animal to recognize its nutritional status and partition nutrients accordingly, should prove fruitful to understanding causes of variations of milk production in response to feed quantity and quality. Several substrates show increased mammary arteriovenous difference with increasing blood concentrations. This may reflect differing ratios of blood flow: milk yield. The steep gradient of concentration of substrates across the mammary epithelial cell membrane suggests that a major impediment to substrate supply for milk synthesis is the rate of substrate transport across the membrane.

Original languageEnglish (US)
Pages (from-to)1041-1058
Number of pages18
JournalJournal of dairy science
Volume68
Issue number4
DOIs
StatePublished - Jan 1 1985

ASJC Scopus subject areas

  • Food Science
  • Animal Science and Zoology
  • Genetics

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