Endocrine Control of Energy Metabolism in the Cow: Correlations of Hormones and Metabolites in High and Low Yielding Cows for Stages of Lactation

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Abstract
Measures of hormones and metabolites in blood plasma of high and low yielding cattle matched for diet and stage of lactation were investigated for relationships between milk yield, body weight and concentrations of hormones (prolactin, growth hormone [GH], insulin and thyroxine [T4]) and metabolites (glucose, nonesterified fatty acids, .beta.-hydroxybutyric acid and L-lactic acid) for stages of lactation. A 1st approach correlated total milk yields of 15 cows with average constituents during the four 24-h blood samplings through the first 27 wk of lactation. The 2nd examined associations of changes with sampling periods in milk yield or body weight with changes in hormones and metabolites. Total milk yield of the high yielding group was correlated positively with ratios of GH/T and glucose/T and correlated negatively with T. Changes in GH and its ratio to insulin and changes in yield were correlated positively for groups combined. Changes in T were correlated negatively with changes in yield. Changes in liveweight gain were related positively to insulin and lactic acid and negatively with changes in GH. Changes in GH were related positively to changes in nonesterified fatty acids.