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Effect of supplemental dietary slow‐release urea on growth performance and physiological status of dairy heifers

Zhang, Jiaojiao, Qiu, Qiang, Shang, Zhanhuan, Liu, Shujie, Degen, Allan, Li, Shanshan, Yan, Qi, Wang, Weiwei, Jing, Xiaoping, Bai, Yanfu, Ding, Luming
Animal science journal = 2018 v.89 no.7 pp. 966-971
Holstein, ammonium nitrogen, average daily gain, blood serum, calves, dairy heifers, dry matter intake, fatty acid composition, free fatty acids, growth performance, health status, physiological state, roughage, rumen fermentation, urea, urea nitrogen, volatile fatty acids
We examined the effect of supplemental dietary slow‐release urea on the growth performance and physiological status of 16 dairy Holstein heifers (10 months of age, 322 ± 10 kg). The heifers were offered a formulated isocaloric and isonitrogenous 70:30 roughage : concentrate ration and were assigned randomly to one of four levels of slow‐release urea supplementation (0% [U₀], 1% [U₁], 1.5% [U₁.₅] and 2% [U₂] dry matter [DM]). The total study lasted 95 days, which included a 20 days adaptation period. Dry matter intake (DMI) of U₂ was lower than the intakes of U₀ and U₁ (p < .05), while average daily gains (ADG) of U₁ and U₁.₅ were higher than U₀ and U₂ (p < .05). Rumen volatile fatty acids concentration did not differ among the four treatments, while ammonia nitrogen concentration increased with an increase in urea level (p < .05). Serum blood urea nitrogen concentration was lower in U₁.₅ than in U₀ and U₂ while serum free fatty acids concentration in U₂ was higher than in the other three treatments (p < .05). We concluded that the addition of urea at a level of 1.5 to 2.0% DM resulted in a reduction in DMI but the addition of 1.0%–1.5% urea resulted in the highest ADG, with no negative effects on rumen fermentation and health status of the calves.