Comparison of milk production and endocrine profiles of dairy cows exposed to either white light-emitting diode or induction lighting.

White light-emitting diodes (WLEDs) are characterized by their high blue light intensity, whereas induction lighting (IL) emits lower levels of blue light. This study investigated the effects of exposure to WLED and IL on milk production and physiological responses in dairy cows. Nine lactating Holstein cows [225 ± 32.5 days in milk, 710 ± 24.6 kg initial body weight (BW), 2.6 ± 1.6 parity] were kept under a 16:8 h light-dark cycle and assigned to two treatments for 3 wk each in a 2 × 2 crossover design: exposure to either WLED (443 nm peak wavelength, 231 lx) or IL (529 nm peak wavelength, 237 lx). During the dark period, light intensity was 0.0 lx. All cows were fed total mixed ration ad libitum. Milk samples were collected weekly, and serial blood sampling was performed on the last day of each treatment. Dry matter intake, BW, milk yield, and milk composition did not differ between treatments. However, plasma non-esterified fatty acids concentration tended to be higher for the WLED than for the IL (P = 0.09). In addition, plasma melatonin and cortisol concentrations were higher (P < 0.01) for the WLED group than for the IL group. These findings suggest that differences in light wavelength between WLED and IL affect melatonin and cortisol secretion and may also impact lipid metabolism, without altering milk production performance.