Effects of Photoperiod Management on Milk Production in Lactating Dairy Cows

The goals of this research were to evaluate the interaction effects between photoperiod management and dietary grain allocation in lactating dairy cows and to determine if any relationships exist between photoperiod management and the persistency of lactation in selected dairy herds in Alberta. In study 1, there were no significant interaction effects between photoperiod management and dietary grain allocation on milk production, dry matter intake or body weight gain. Cows that were exposed to long day photoperiod (LP; 16 h of light, 8 h of darkness) increased milk yield by 2. 2 kg/d relative to the animals exposed to short day photoperiod (SP; 8 h of light, 16 h of darkness). However, galactopoietic responses to LP were only detected four weeks after initial light exposure; when cows were fed different diets, after adaptation to light treatment, the effect of LP on milk yield was not detected. Contrarily, cows fed high grain diets increased milk yield and dry matter intake compared with those fed low grain diets. In study 2, we found that animal exposure to light did not differ between summer and winter. Thus, farms that practiced photoperiod management were able to provide long day photoperiod throughout the year whereas cows in farms without photoperiod management were exposed to short photoperiod even in the summer months. The current study showed that persistency of lactation was not different for farms with photoperiod management compared with farms without it. Long day photoperiod can increase milk production in lactating dairy cows but animal responses may be affected to a greater extent by other management practices.