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Prepartum shifting light circadian rhythm disruptions cause insulin resistance in periparturient dairy cows.

C. J. McCabe


Prepartum shifting light circadian rhythm disruptions cause insulin resistance in periparturient dairy cows.
C. J. McCabe*, A. Suarez-Trujillo, T. M. Casey, J. P. Boerman. Department of Animal Sciences, Purdue University West Lafayette, IN.

Circadian clocks function to maintain homeostasis. Disruption of clocks by altering timing of external cues affects glucose metabolism in humans and rodents, with long-term disruption associated with development of metabolic diseases. The objective of this experiment was to analyze the effect of exposure to chronic light-dark cycle phase shifts from 5 weeks before expected calving (BEC) to parturition on glucose tolerance at 2 weeks prepartum and 1 week postpartum in dairy cows. Multiparous Holstein cows (n = 16) were exposed to 16 h of light and 8 h of dark (CON) or phase shifting (PS) of the start of the light cycle 6 h every 3 d beginning 35 d BEC. Following calving, both treatments were exposed to control lighting through 60 DIM. At 14 d BEC and 7 DIM, intravenous glucose tolerance tests were performed with a dose of 250 mg/kg BW of a 50% dextrose solution. Before dextrose administration, cows were fasted for one hour and baseline blood samples were taken at 15 and 5 min before administration to determine Revised Quantitative Insulin Sensitivity Check Index (RQUICKI). We observed no difference in insulin sensitivity between treatments at both physiological stages via RQUICKI (P > 0.05). Following dextrose administration, blood samples were taken at 14 time points over 3 h to quantify blood glucose, BHBA, insulin, and NEFA. Linear mixed model analysis indicated no effect of treatment on blood glucose by time point or area under the curve (AUC) for both stages (P > 0.05). At 14 BEC, there was no difference in baseline values, but insulin AUC was higher in PS compared with CON (P = 0.05; 4,302.8 vs. 2,386.3 ng/mL/180 min). At 7 DIM, there was no effect of treatment on glucose AUC (P = 0.71), but the difference in insulin AUC between PS and CON (P = 0.03; 1,052.9 vs. 697.1 ng/mL/180 min) was maintained. There was no effect of treatment on BHBA nor NEFA, but there was an interaction between treatment and time for NEFA at 7 DIM (P = 0.007). CON vs PS cows produced more milk through 60 DIM (42.6 vs. 40.3 kg/d; P = 0.05). Exposure to chronic light-dark PS in late gestation decreased insulin sensitivity in periparturient cows, which may influence milk production.

Keywords: insulin sensitivity, glucose tolerance test, circadian rhythm.