Mammary core clock gene expression is impacted by photoperiod exposure during the dry period in goats

Short-day photoperiod (SDPP) during the dry period increases milk production compared to long-day photoperiod (LDPP) in goats. Photoperiod information is sent to the master clock in the suprachiasmatic nuclei (SCN), which send temporal information to peripheral clocks located in every tissue of the body. We hypothesized photoperiod effects on milk production are mediated in part by changes in mammary clocks. Our objective was to determine the effect of photoperiod manipulation during the dry period in goats on core clock genes expression in mammary gland. Multiparous goats (n = 6) were blocked at dry off into two treatments: LDPP and SDPP. Serial mammary biopsies were taken over a 24 h period during three weeks prepartum. Total RNA was isolated, and q-PCR analysis of the core clock genes CLOCK, ARNTL, PER1, CRY1, and CRY2 found exposure to LDPP significantly increased ARNTL (P <.05) expression relative to SDPP exposure. Plasma prolactin levels were significantly increased (P <.05) after seven weeks of photoperiod treatment, but not at three weeks prepartum. The mechanism and significance of photoperiod-induced changes in mammary clock also need to be elucidated but may be related to seasonal changes in lactation.