Physiological state and photoperiod exposures differentially influence circadian rhythms of body temperature and prolactin and relate to changes in mammary PER1 expression in late pregnant and early lactation dairy goats

Abstract

Abstract Short-day photoperiod (SDPP; 8 h light:16 h dark) during the dry period increases milk production compared with long-day photoperiod (LDPP; 16 h light:8 h dark). We hypothesized that the impact of photoperiod on lactation is mediated by alterations in the circadian system. Twelve Saanen goats were blocked at dry off into SDPP (n = 6) and LDPP (n = 6) treatments and mammary biopsies were taken in the middle of light and dark phases at 3 wk prepartum and 5 wk postpartum. Total RNA was isolated, and the expression of clock genes was analyzed by qPCR. SDPP goats produced more milk than LDPP goats (3.15 ± 0.04 vs. 2.7 ± 0.05 kg/d). In the 24 h period, LDPP goats had a greater body temperature than SDPP goats at 3 wk prepartum (39.6 ± 0.06 vs. 39.3 ± 0.1 °C) and 5 wk postpartum (40.1 ± 0.15 vs. 39.7 ± 0.1 °C). Cosinor analysis revealed that physiological state affected body temperature mesor (P