Meal patterns and meal-induced metabolic changes in calves fed milk ad lib

The feeding behavior of 11 calves fed milk ad lib was characterized and analyzed at the age of 5 weeks, and the short-term changes in the plasma concentrations of various metabolites (glucose, lactate, free fatty acids, triglycerides, beta-hydroxybutyrate) and insulin in relation to a representative spontaneous milk meal were measured during the following week. In a 6-day period, the calves consumed 287 (=86%) of a total of 335 milk meals during the light phase from 0500-2200 [on average, 4.4 +/- 0.5 (mean +/- SEM) meals]. The meal size and duration during light were 2.0 +/- 0.3 kg and 5.3 +/- 0.3 min, respectively. However, only 0.7 +/- 0.1 milk meals of similar size and duration were consumed during the dark phase. The plasma concentrations of insulin and glucose increased in response to the spontaneous milk meal and remained elevated for at least 2 h after meal end. The plasma concentrations of triglycerides, free fatty acids, and beta-hydroxybutyrate also increased after meal termination, and remained elevated until 40 min (triglycerides, free fatty acids) and 60 min (beta-hydroxybutyrate) after meal end, respectively. The observed spontaneous milk intake patterns were similar to the natural suckling behavior described for calves, suggesting that the conditions of the present experiment did not disrupt the animals' natural feeding behavior. Some of the profound metabolic changes in relation to a spontaneous milk meal might contribute to the control of milk intake in calves, but further experiments are necessary to test this idea.