Effects of the Switch From a Short-Day Photoperiod With Natural Light to a Long-Day Photoperiod With White Light-Emitting Diode or Induction Lighting on Milk Production and Endocrine Profiles in Lactating Dairy Cows.

This study evaluated the response of milk production and endocrine profile to a switch from short-day photoperiod (SDPP) with natural light to long-day photoperiod (LDPP) with white light-emitting diode (WLED) or induction lighting (IL) in lactating dairy cows. Nine Holstein cows (198 ± 10.0 days in milk) were initially exposed to SDPP of 10:14 h light-dark cycle (10L:14D) with natural light (SDPP period), followed by a long-day photoperiod (LDPP; 16L:8D) using either WLED (443 nm peak, LDPP-W, n = 5) or IL (IL; 529 nm peak, LDPP-I, n = 4). Each period comprised a 1-week adaptation and a 2-week sampling period. Milk yield decreased after switching to LDPP-W (p < 0.05) but remained unchanged with LDPP-I. The slope of milk yield over the entire trial period (from the beginning of SDPP to the end of LDPP period) differed depending on lighting type (p = 0.05), being negative in the LDPP-W and positive in the LDPP-I. Plasma prolactin concentration in the light period increased after switching to LDPP-I but not to LDPP-W. These results indicate that LDPP using IL is likely more effective in promoting milk yield than WLED, potentially due to enhanced prolactin secretion.