Contents lists available at ScienceDirect Livestock Science journal homepage: www.elsevier.com/locate/livsci 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 S. Marti a, ⁎ , C. Medinya b , A. Pérez c , M. Verdú d , A. Solé a , B. Quintana a , M. Devant a a IRTA, Ruminant Production, Caldes de Montbui 08140, Barcelona, Spain b Soluciones Integrales para la Nutrición Animal S.L., Sallent, Barcelona, Spain c Piensos Procasa S.A., 43206 Reus, Tarragona, Spain d bonÀrea Agrupa, 25210 Guissona, Lleida, Spain ARTICLE INFO Keywords: Beef Behavior Performance Photoperiod modification Prolactin 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 con- formation 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 mod- ification as sexual behaviors could increase the risk of carcass bruising impairing carcass quality. 1. Introduction Seasonal naturally changing day length may influence growth of calves over the year (Mossberg and Jönsson, 1996) as observed ana- lyzing a retrospective database collected during 2012 and 2015 on Holstein bulls feed high concentrate diets in Spain (Fig. 1). Under- standing that in free-range conditions most of the eating takes place during the day, photoperiod modification could be a strategy to im- prove growth rate by increasing the time that calves spend eating and therefore increasing total intake (Peters et al., 1978). Some authors found an increase of growth rate with an increase of daylight hours (Peters et al., 1978; Petitclerc et al., 1983; Small et al., 2003) as long- day photoperiod may increase average daily gain (ADG) due to mod- ification of melatonin secretion and circulating prolactin, growth hor- mone and IGF-1 (Dahl et al., 2000), while others did not (Zinn et al., 1989; Kennedy et al., 2004). These variations could be due to age, production phase, gender and photoperiod strategies used in these studies. In addition, rearing intact bulls in intensive production systems for meat have management difficulties and risk of increased carcass brushing and dark-cutting meat produced by their sexual and ag- gressive activity (Mach et al., 2009). Some authors observed that an increase of daylight hours had an effect on animal behavior by reducing https://doi.org/10.1016/j.livsci.2020.104020 Received 5 December 2019; Received in revised form 23 March 2020; Accepted 24 March 2020 ⁎ Corresponding author. E-mail address: sonia.marti@irta.cat (S. Marti). Livestock Science 238 (2020) 104020 Available online 14 April 2020 1871-1413/ © 2020 Elsevier B.V. All rights reserved. T