| Summary: | The aim of this study was to evaluate the effect of production system on the health, performance, carcass characteristics, and meat quality of autumn born (AB) and spring born (SB) Holstein bulls. The study involved a total of 224 Holstein bulls and was conducted over two years (2017/18, 2018/19). The four production system treatments differed during the grower period and consisted of: (i) grazed with no concentrate supplementation (G), (ii) grazed with 2 kg concentrate supplementation per day (G2), (iii) grazed with ad libitum access to concentrates (GA) and (iv) housed with ad libitum access to concentrates and grass silage (HA). All bulls were finished on ad libitum concentrates and grass silage and were slaughtered at a mean age of 15.5 months. Total grower dry matter intake (DMI) (<i>p < </i>0.001) and total finishing DMI (<i>p < </i>0.001) differed between production systems for both AB and SB bulls, with that of GA bulls being the greatest in both cases. Average daily gain (ADG) during the grower period was greatest (<i>p < </i>0.001) for the HA production system in the AB bulls and the GA and HA production systems for the SB bulls. However, during the finishing period, G bulls had the greatest (<i>p </i>< 0.001) ADG of the AB bulls, while that of the SB bulls was from the G2 production system (<i>p < </i>0.001). For both AB and SB, bulls on the GA and HA production systems produced heavier cold carcass weights than the G and G2 bulls (<i>p < </i>0.001). There was no significant difference (<i>p</i> > 0.05) in health, carcass conformation, fat classification, or meat quality between production systems.
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