Abstract
N-carbamylglutamate (NCG), an alternative of arginine, has been applied to improve nitrogen utilization by promoting the synthesis of urea and nitric oxide in dairy cows. However, scarce data on the effects of NCG on bulls exist, especially on antioxidant and immunity status and rumen fermentation. This study was conducted to investigate the effects of NCG on growth performance, nutrient digestibility, antioxidant and immunity status, and rumen fermentation patterns in finishing Holstein bulls. Forty-five healthy Holstein bulls with initial body weight (BW) of 478 ± 13.7 kg were assigned to a randomized complete design with 3 treatments. The NCG supplementation was 0, 15, or 25 g/d per bull in the three different treatments. The experimental period was 122 d, after a-7 d adaptation period. Although the final BW and average daily gain were not affected by NCG supplementation, dry matter intake tended to decrease linearly, and feed to gain ratio decreased linearly with increasing NCG supplementation. The apparent total tract digestibility of dry matter, organic matter, non-fiber carbohydrate were not affected, whereas a linear increase was observed in acid detergent fiber and neutral detergent fiber digestibility, and a quadratic increase was observed in crude protein digestibility. The concentration of total protein and nitric oxide was greater in bulls fed 15 g/d and 25 g/d NCG than in control. The serum total anti-oxidant capacity increased quadratically with increasing NCG supplementation, and peaked at 15 g/d. The interleukin-2 concentration significantly increased in bulls fed 15 g/d NCG. The concentration of total volatile fatty acids was greater in bulls fed 15 g/d NCG compared to the other groups. In conclusion, NCG supplementation in finishing Holstein bulls may be beneficial for the improvement of feed efficiency, by increasing feed digestibility and improving antioxidant and immunity status. The most optimal dose appeared to be 15 g/d.
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