Effects of a progressive or an abrupt increase of hours of light exposition in fall-winter months in finishing Holstein bulls fed high-concentrate diets

Abstract

A total of 218 Holstein bulls were used to evaluate the effect of a progressive (Experiment 1; n = 106; 335 ± 4.3 kg of BW, and 243 ± 0.1 d of age) and an abrupt (Experiment 2; n = 105; 352 ± 6.7 kg of BW, and 244 ± 2.6 d of age) increase of daylight hours. In experiment 1, bulls were randomly allocated in 2 treatments according to natural photoperiod (NP) or progressive increase of daylight hours (PP) for 84 d of study. In experiment 2, bulls were randomly allocated in 2 treatments according to natural photoperiod (NP) or abrupt increase of daylight hours (AP) for 70 d of study. A computerized concentrate feeder was used to record daily concentrate intake and eating behavior. Body weight and animal behavior was recorded every 14 d until bulls were transported to the slaughterhouse. Blood samples were collected on d 0, 28, 56, and at the end of the study for serum prolactin determination. At slaughter, hot carcass weight and degree of carcass fatness and conformation were recorded. Data were analyzed using mixed models with treatment, time and its interaction as main effects, and the interaction between treatment and pen and the 3-way interaction between treatment, pen and period as random effects. Progressive or abrupt increase of daylight hours up to 16 h a day did not improve weight gain and did not modify total feed intake. In experiment 1, PP calves increased (P < 0.05) number of meals a day while meal size and meal duration decreased (P < 0.001); PP increased lying and rumination time, reduced number of fights, attempts to mount and mounts (P < 0.05) compared with NP. PP bulls tended (P < 0.10) to have a greater percentage of carcasses classified as poor conformation and low fatness scores than NP bulls. In experiment 2, AP calves had more (P < 0.05) attempts to mount and mounts compared with NP. AP bulls increased (P < 0.05) one meal per day compared with NP bulls. Serum prolactin concentration increased (P < 0.05) in PP and AP compared with NP calves. Carcass conformation and fatness did not differ between AP and NP. Progressive photoperiod modification could be used as a strategy to reduce sexual and aggressive behaviors although carcass quality may be impaired. Caution should be taken with abrupt photoperiod modification as sexual behaviors could increase the risk of carcass bruising impairing carcass quality.