Interaction effect of photoperiod management and dietary grain allocation on productivity of lactating dairy cows

Abstract

The objective of this study was to determine the interaction effects of photoperiod management and dietary grain allocation on the productivity of lactating dairy cows. Sixty Holstein cows in mid-lactation (days in milk = 113 ± 36.0; mean ± SD) were assigned to either a long photoperiod (LP; 16 h light) or a short photoperiod (SP; 8 h light) treatment. After a 30 d light adaptation period, cows within each photoperiod treatment were fed three diets differing in the grain content (15%, 25%, and 35% of dietary dry matter) in a 3 × 3 Latin square design. Cows exposed to the LP increased milk yield compared with those exposed to the SP (39.0 vs. 36.8 kg d−1) after a 30 d of light adaptation period. Although the positive effect of LP was not sustained after cows were assigned to dietary treatments in a 3 × 3 Latin square design, cows fed the 35% grain diet increased fat-corrected milk yield compared with those fed 25% or 15% grain diet (35.9 vs. 33.4 or 32.9 kg d−1, respectively). This study indicated that LP management and feeding high grain diets did not lead to synergistic effects on productivity of dairy cows.