Resumo

BERETTA, V.; SIMEONE, A.; MORTEIRO, I.  e  YOUNG, I.. Effect of crude protein level in high grain diets on calf growth and feed utilization. Agrociencia Uruguay [online]. 2020, vol.24, n.2, e111.  Epub 01-Dez-2020. ISSN 1510-0839.  https://doi.org/10.31285/agro.24.111.

This study assessed the effect of crude protein level in the diet on animal performance, feed conversion ratio and N utilization, in early-weaned lot-fed calves. Four iso-energetic rations were formulated (me: 12.0 MJ/kg dm) differing in the crude protein content (cp: 12%, 15%, 17% and 21%, dm basis), and offered in a random experimental design to 24 Hereford calves (107.2 ± 21.5 kg). Animals were individually housed and fed ad libitum twice a day for 84 days. Increasing cp levels in the diet promoted a quadratic response (P<0.01) for dry matter intake (kg/d) and liveweight gain (lwg, kg/d), with maximum lwg of 1.36 kg/d for cp= 17.5%, without differences in subcutaneous back fat thickness (3.70 ± 0.73 mm, P = 0.25) or feed conversion ratio (4.44 ± 0.26, P> 0.10). As cp increased in the diet, N consumption increased quadratically (P <0.01), and an improvement was observed for cp (P = 0.053) and ndf (P = 0.020) apparent digestibility. Daily excretion of N in feces tended to decrease (P = 0.06), while urea-N concentration both in blood (P = 0.013) and urine (P = 0.046) increased. These results show that a level of 17% cp in the diet would optimize the performance of lot-fed early-weaned beef calves while controlling the excretion of N to the environment.

Palavras-chave : calves; early weaning; growth; intake; N utilization.

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