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Light-dark phase shift circadian disruption does not affect cortisol and progesterone concentrations in periparturient dairy cows.

A. Suarez-Trujillo

Abstract:

53
Light-dark phase shift circadian disruption does not affect cortisol and progesterone concentrations in periparturient dairy cows.
A. Suarez-Trujillo*1, J. Franco2, T. Steckler1, J. Boerman1, K. Plaut1, T. M. Casey1. 1Department of Animal Sciences, Purdue University West Lafayette, IN, 2Metabolite Profiling Facility, Bindley Bioscience Center, Purdue University West Lafayette. IN.

Circadian-metabolic-reproductive systems are integrated and reciprocally regulated. Circadian clocks set the daily rhythms of multiple hormones that influence metabolism and reproduction. Currently, there is little understanding regarding how reproductive state effects circadian clock function, and how circadian clocks regulate metabolism during pregnancy and lactation. A previous study showed that exposure to chronic light-dark phase shifts (PS) during the dry period in dairy cows resulted in loss of the centrally generated circadian rhythms of melatonin and core body temperature, as well as decreased blood glucose and increased overall melatonin levels. These changes were related to increased milk production postpartum. The objective of this study was to measure cortisol (CORT) and progesterone (P4) in the transition period dairy cows exposed to PS to determine how altering central clock function effects these metabolic and reproductive hormones. Beginning 5 wk before expected calving (BEC) multiparous cows were assigned to control (n = 16) and exposed to 16h light: 8h dark or phase-shifted (n = 16) by 6h every 3d until parturition. All cows were exposed to control lighting after calving. Blood samples were taken at 0600 on d 35 BEC, 21 BEC, 2 BEC, and d 0, 2, 9, 15 and 22 postpartum. A subset of cows (n = 6/group) were sampled every 4 h over 48 h at 3 time points: d 23 BEC, 9 BEC, and 5 DIM, and data was analyzed for fit to 24 h rhythm in R cosinor analysis. CORT and P4 were measured using LC MS/MS. Two-way ANOVA analysis of the concentration of CORT and P4 found no effect of treatment (CORT P = 0.48; P4 P = 0.52). Cosine analysis of CORT and P4 concentration determined that neither treatment showed circadian rhythms in the 3 studied periods. Results suggest that CORT or P4 levels cannot account for treatment differences in milk yield and glucose. Lack of circadian rhythms in of hormone levels suggest that in periparturient cows 24 h profiles of CORT and P4 levels reflect reproductive state, and this milieu may mask circadian rhythms.

Keywords: circadian rhythms, cortisol, progesterone.