Effects of thyroxine and growth hormone treatment of dairy cows on milk yield, cardiac output and mammary blood flow.

S. R. Davis, R. J. Collier, J. P. McNamara, H. H. Head, W. Sussman

Research output: Contribution to journalArticlepeer-review

75 Scopus citations

Abstract

Four cows received thyroxine injections (T4; 20 mg/d) and three cows received growth hormone injections (GH; 44 mg/d) for 4 d during successive 16-d experimental periods. Measurement was made of milk yield, protein yield, mammary tyrosine and phenylalanine uptake, blood plasma hormone concentrations, mammary blood flow and cardiac output. Milk yield increased by 25% with T4 and 21% with GH treatment. Milk protein content tended to decline during T4 treatment and increase following GH treatment. Cardiac output increased by 8.9 liter/min (20%) and 4.6 liter/min (10%) with T4 and GH injection. Mammary blood flow (half-udder) increased from 3.6 to 4.9 liter/min (35%) and from 3.3 to 4.4 liter/min (33%) with T4 and GH treatment, respectively. These increases calculated on a whole-udder basis, accounted for 28% (T4) and 48% (GH) of the increases in cardiac output. The proportion of cardiac output perfusing the (whole) udder increased to 19.1% (T4) and 18.7% (GH), increases of 17 and 30%, respectively. Heart rate increased with T4 (but not GH treatment) from 80 to 115/min. Ratio of blood flow to milk yield was not changed by either treatment. The proportion of cardiac output perfusing the udder likely plays a major role in facilitating the partitioning of nutrients for milk synthesis.

Original languageEnglish (US)
Pages (from-to)70-79
Number of pages10
JournalJournal of animal science
Volume66
Issue number1
DOIs
StatePublished - Jan 1988

ASJC Scopus subject areas

  • Food Science
  • Animal Science and Zoology
  • Genetics

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