The effects of overstocking Holstein dairy cattle during the dry period on cortisol secretion and energy metabolism

Abstract

The objective was to determine whether overstocking during the dry period could alter physiological parameters in dairy cattle associated with cortisol secretion and energy metabolism. Four groups of 10 late-gestation, nonlactating Holstein cows (6 multiparous cows and 4 heifers per group) were exposed to both a control [1 lying stall/cow and 0.67m of linear feed bunk (FB) space/cow] and an overstocked (1 stall/2 cows and 0.34m of FB space/cow) stocking density treatment in a replicated crossover design with 14-d treatment periods. On d 1, 3, 5, 7, 9, and 11 of each 14-d treatment period, blood and fecal samples were collected from each cow for the determination of plasma nonesterified fatty acids (NEFA), glucose, insulin, and fecal cortisol metabolite (11,17-dioxoandrostane; 11,17-DOA) concentrations. Glucose and ACTH challenges were conducted on d 13 and 14, respectively, of each treatment period. Dry matter intake per cow was greater during the overstocked period than during the control period (15.9 vs. 14.9±0.5kg/d). Plasma NEFA and glucose concentrations were greater (0.11 vs. 0.09±0.006mEq/L and 65.3 vs. 64.2±1.1mg/dL, respectively) and 11,17-DOA concentration tended to be greater (891 vs. 792±86ng/g of fecal dry matter) during the overstocked period than during the control period. Insulin concentration was the same during the overstocked (29.0±2.1μIU/mL) and control (31.2±2.1μIU/mL) periods. Overstocking was associated with slightly slower glucose clearance from circulation as evidenced by a greater area under the curve estimate for the glucose response curves (2,882 vs. 2,657±165mg/dL × 180min) but a more attenuated insulin response (insulin area under the curve = 5,258 vs. 6,692±1,104μIU/mL × 180min for the overstocked and control periods, respectively). Changes in tissue glucose uptake may be mediated by changes in pancreatic insulin secretion or peripheral tissue responses to insulin. The role of glucocorticoids in mediating these changes in energy metabolism is still unclear because stocking density treatment was not associated with changes in adrenal secretion of cortisol following ACTH stimulation.