Effects of concentrate proportion and protein supplementation on performance of growing and finishing crossbred bulls fed a whole-crop barley silage-based diet

Abstract

A 2 × 3 factorial design was used to study the effects of concentrate proportion and protein supplementation on performance of growing and finishing bulls fed a whole-crop barley silage (WCBS)-based diet. A feeding experiment comprised 30 crossbred bulls with average initial liveweight of 315 kg. The bulls were offered WCBS ad libitum. The two concentrate proportions were 200 and 400 g/kg diet dry matter (DM). The concentrate used was (1) rolled barley, (2) rolled barley plus rapeseed meal or (3) rolled barley plus urea-based supplement. The crude protein (CP) content of rolled barley was 119 g/kg DM and both protein supplements were given so that the CP content of the concentrate was raised to 170 g/kg DM. The final liveweight of the bulls was 669 kg, on average, and it was not affected by dietary treatments. The dietary treatments had no effects on total DM intake of the bulls (8.91 kg/day). However, the increasing concentrate proportion increased energy intake (P < 0.05), carcass gain (P < 0.01) and dressing proportion (P < 0.05) and improved carcass conformation (P < 0.05). Protein supplementation had no effects on energy intake, carcass gain, dressing proportion or carcass conformation but it tended to increase carcass fat score (P = 0.06) compared to the bulls fed without protein supplementation. Overall, the results indicate that there is no reason to use protein supplementation for growing and finishing bulls more than 300-kg liveweight when they are fed with good quality whole-crop barley silage and barley-based concentrate.