Effect of feed delivery time and concentrate level on rhythms of plasma metabolite, enzyme, and hormone levels, glucose tolerance and milk production in dairy cow

The objective of the first study was to determine the effects of evening feeding (2100h) versus morning feeding (0900h) on plasma hormone, enzyme and metabolite levels and glucose tolerance in high-producing dairy cows in two separate experiments. Shifting the delivery of fresh TMR to 2100h from 0900h shifted and increased the variability of diurnal rhythms in plasma glucose, insulin, cholesterol, liver enzymes but not melatonin levels. Glucose tolerance tests performed at 3, 10, 15 and 22 hours post-feeding showed that peak glucose and insulin response varied with hours post-feeding. This is the first study to demonstrate the effect of hours post-feeding on glucose tolerance in dairy cows. The objective of the second study was to examine the production response to evening feeding. The effect of evening feeding on patterns of plasma insulin and glucose levels at 2 and 14 hours post-feeding were similar to those observed during the first study. An unexpected low milk fat content (1.7%) may have masked any possible beneficial effects of evening feeding on production.