Effects of Supplements with Different Protein Contents on Nutritional Performance of Grazing Cattle During the Rainy Season

Effects of Supplements with Different Protein Contents on Nutritional Performance of Grazing Cattle During the Rainy Season

Animal Bioscience, March 2016

27004813

J. F. Figueiras, E. Detmann, M. O. Franco, E. D. Batista, W. L. S. Reis, M. F. Paulino, S. C. Valadares Filho

The objective of this study was to evaluate the effects of supplements with different crude protein (CP) contents on grazing cattle intake, digestibility, ruminal fermentation pattern, and nitrogen metabolism characteristics during the rainy season. Five ruminally and abomasally cannulated Holstein × Zebu steers (296 kg BW) were used in a 5 × 5 Latin square design. The animals grazed five signal grass paddocks (0.34 ha). The five treatments evaluated were: control (no supplement) and 1.0 g of supplement/kg BW with 0, 330, 660, and 1,000 g of CP/kg as-fed. The supplement was composed by starch, soybean meal, urea, and ammonium sulphate. There was a positive linear effect (P≤0.033) of the CP content in the supplements on the organic matter (OM), CP, and digested OM intakes. The provision of supplements did not increase (P≥0.16), on average, total and ruminal digestibilities of OM and CP. However, the increase in CP content in the supplements caused a positive linear effect (P≤0.018) on ruminal digestibilities of OM and CP. Additionally, a quadratic effect of the CP contents of the supplements were observed (P=0.041) for the ruminal digestibility of NDFap, with the highest estimate obtained with the CP content of 670 g/kg. The supply of supplements increased (P<0.001) the ruminal ammonia nitrogen concentration, which also changed linearly and positively (P<0.001) according to increase in CP content in the supplements. The apparent N balance and relative N balance (g/g N intake) were not, on average, changed (P≥0.164) by the supplements supply. However, both showed a tendency of a linear increase (P≤0.099) with increasing supplement CP content. The supplements supply increased (P=0.007) microbial nitrogen production in the rumen, which also changed linearly and positively (P<0.016) with increasing supplement CP content. In conclusion, protein supplementation in grazing cattle during the rainy season, while stimulate voluntary forage intake, results in higher efficiency of nitrogen utilization when compared to energy supplementation. This is a possible response to increased microbial protein synthesis in the rumen and improved nitrogen status in the animal body.