Response to Intravenous Glucose Challenges in Dairy Cows Fed Different Amounts of a Total Mixed Ration in the Dry Period

The feeding regime during the dry period has often a marked impact on the metabolism during the post-parturient period in dairy cows. In the present study the response to intravenous glucose challenges was tested in cows given different amounts of a total mixed ration (TMR) during the dry period. Multiparous high yielding cows (N = 24) were divided into three equal groups. The groups were offered TMR corresponding to 70, (Low intensity) 110 (Medium intensity) or 170 (High intensity) MJ ME/day during the eight weeks dry period. After parturition all cows were offered an other TMR ad libitum during the first twelve weeks. The energy in the TMR offered during the dry period contained 11.8 MJ ME/kg DM and the TMR offered during the lactation contained 12.2 MJ ME/kg DM. Feed intake, body weight and body condition scoring was monitored during the experiment. Blood was regularly analysed for key metabolites and hormones. Glucose challenges were performed three weeks prepartum and three weeks postpartum. The cows were injected with 150 mg glucose/kg body weight in the jugular vein. Blood was then collected frequently for one hour. The rate of glucose disappearance prior to parturition was 2.4, 2.7 & 4.1%/min for the low, medium & high intensity fed groups respectively. The high intensity fed cows were markedly hyperinsulinemic. However, the insulin response to the glucose challenge, calculated as the area under the response curve (AUC), did not differ between the 3 treatments. Cows which were subjected to the high intensity feeding during the dry period showed a pronounced reduction in feed intake and a deeper nadir of negative energy balance after parturition. In cows which were fed the low and medium intense dry period diets the glucose disappearance rate increased with 150% as compared to the dry period. The increase was much less, about 30%, in cows fed the high intensity diet during the dry period. The insulin response to the glucose challenge was reduced to one third of the response prior to parturition regardless of treatments in the dry period.

These results suggest that the glucose disappearance rate is strongly influenced by the level of feed intake. The pancreatic insulin response to glucose was markedly reduced in the post-partal period in all three treatments. Overfeeding in the dry period led to a deeper and longer period of negative energy balance post partum but the pancreatic insulin response to glucose was not affected.