METABOLITE AND HORMONAL RESPONSES TO GLUCOSE OR PROPIONATE INFUSIONS IN PERIPARTURIENT DAIRY-COWS SUPPLEMENTED WITH CHROMIUM

Two studies were conducted to evaluate the effects of Cr supplementati on on blood metabolite and hormonal responses of Holstein cows to gluc ose challenges during late pregnancy and early lactation and to propio nate challenges during early lactation. Eight multiparous and 4 primip arous cows (Experiment 1) and 12 primiparous cows (Experiment 2) were assigned to one of two treatments: control and 0.5 ppm of supplemental Cr. The glucose challenges were performed at 2 wk prepartum and at 2 wk postpartum, and the propionate challenges were conducted at wk 2 an d 6 postpartum During glucose tolerance tests, Cr supplementation redu ced the ratio of insulin to glucose and reduced plasma concentrations of insulin and triglycerides of primiparous cows during the prepartum period. Chromium supplementation decreased plasma Cr of primiparous co ws following glucose challenge. With supplemental Cr, insulin sensitiv ity was reduced postpartum, particularly for primiparous cows, but ins ulin sensitivity was increased prepartum. Results of this study sugges ted that primiparous cows experienced Cr deficiency during late pregna ncy and possibly during early lactation. Following propionate infusion , Cr supplementation increased the serum glucose peak, increased the a rea under the response curve for serum glucose, and tended to increase IGF-I concentrations. Chromium supplementation tended to reduce the r atio of insulin to glucagon. Supplementation might have enhanced gluco neogenesis or glycogenolysis. Supplemental Cr also resulted in reduced variability of most parameters during both experiments.