The Effects Of Two Forms Of Slow-Release Insulin On Lactating Dairy Cow Metabolism And Milk Component Production

Abstract

Milk protein is the most valuable milk component for which dairy producers receive payment. Despite its high value, altering milk protein composition and production in dairy cows by diet has been challenging, particularly as compared to altering milk fat. Improving the efficiency of conversion of dietary nitrogen into productive nitrogen (as milk protein) has both financial and environmental benefits to the dairy industry. Dietary strategies to improve milk protein yield have focused on amino acid requirements, metabolizable protein, and the interaction between dietary energy and protein. However, dietary interventions have had only moderate success in improving milk protein production in well-fed dairy cows. Use of long-term hyperinsulinemic-euglycemic clamps in lactating cows has suggested that milk protein synthesis in dairy cows is not maximized under normal management conditions, as significant improvements in milk protein have been observed in this experimental context. The goal of the present research was to expand on these observations by administering slow-release insulins, from human medicine, to lactating dairy cows. The hypothesis was that administration of slow-release insulins, without provision of supplemental glucose, would increase milk protein production and alter mammary metabolism in lactating dairy cows. In experiment one, two forms of slow-release insulin were tested in a dose response study. Both Humulin-N (H) and insulin glargine (L) exerted insulin-like effects in lactating dairy cows, evidenced by linear decreases of plasma glucose with increasing dose of slow-release insulin. In experiment two, H and L were given twice daily for 10 days to evaluate their effects on milk component production. Milk fat and protein content were both increased by treatment with H and L, suggesting that these forms of slow-release insulin alter metabolism and milk component synthesis. In experiment three, L was used in a mammary metabolism study to examine its effects on mammary uptake and utilization of substrates for protein synthesis. Reduced uptake of both essential and nonessential amino acids was observed during treatment with L, while milk protein yield remained the same for the control and treatment periods. This suggests that L alters metabolism and increases amino acid efficiency of use within the cow.