Plasma insulin and growth hormone in dairy cows; diurnal variation and relation to food intake and plasma sugar and acetoacetate levels.

Abstract

ABSTRACT Marked diurnal variations were found in plasma growth hormone (GH), insulin, acetoacetate (AcAc) and sugar in two herds (U and A) of dairy cows kept at two different levels of feeding. Seven animals from each herd were tested. The main diurnal variations were related to food intake, a significant increase in plasma insulin, and a significant decrease in plasma sugar being found. The acetoacetate level rose significantly during feeding in herd U (moderately underfed), while no significant increase was found in herd A (adequately fed). Plasma growth hormone was found to decrease (P < 0.01) only during feeding in herd U, while no change in the GH level could be detected in herd A. The mean level of GH in herd U was found to be twice the value found in herd A. There were no significant differences between the herds in plasma insulin and sugar. Significant differences in plasma levels of GH, insulin and sugar were found between animals when analysed within the herds. Variations in the levels of insulin and acetoacetate were very small during the night. This is contrary to GH, which shows the least variation during food intake. The correlation coefficient between the plasma components was low, although in many cases significant.