Effects of 4-day hyperinsulinemic-euglycemic clamps during early and mid-lactation on milk yield, milk composition, feed intake, and energy balance

The objective was to determine the effects of insulin on feed intake, milk yield, and milk composition during different stages of lactation. A 4-day hyperinsulinemic-euglycemic clamp was conducted on four multiparous dairy cows starting in weeks 4 and 17 postpartum. Insulin was infused continuously (1 μg/kg, BW/h) and a 50% glucose solution was infused to maintain euglycemia. Feed intake decreased (P < 0.05) by days 3 and 4 of the clamp period while energy balance increased significantly (P < 0.001) during both stages of lactation. Milk (P < 0.05) and energy-corrected milk (P < 0.001) yield decreased during the clamp period in week 4, but not in week 17. The clamp increased (P < 0.05) the concentration and yield of protein and casein during week 17, but not during week 4. The clamp decreased milk urea concentration (P < 0.001) and yield (P < 0.001) in both stages of lactation, but the decrease was most evident in week 17. Fat yield (P < 0.01) and concentration (P < 0.01) decreased during the clamp period in both stages of lactation, but the decrease mainly resulted from a decline in early lactation. The clamp decreased lactose concentration (P < 0.01), but not yield, in both stages of lactation. Citrate concentration (P < 0.01) and yield (P < 0.01) decreased in early lactation only, probably reflecting differences in de novo milk fat synthesis. These results show that the effects of insulin and glucose on energy balance, milk yield and milk composition vary depending upon stage of lactation and, hence, the physiological status of lactating dairy cows.