Does an Excess of Rumen Degradable Protein Improve Performance of Growing Zebu Heifers in Tropical Pasture?

Although concentrations exceeding theoretical requirements may enhance microbial activity, their potential effects on cattle grazing tropical pastures remain to be clarified. The objective of this study is to assess the influence of excess rumen degradable protein (RDP) on feed intake, digestibility and weight gain of Nellore heifers grazing tropical pastures. Forty crossbred heifers (1/2 Nellore x ½ Brahman) with 12 ± 2 months old and 210 ± 27.8 kg were used in completely randomized design. The heifers were allocated to eight 1-hectare paddocks covered with Urochloa brizantha cv. Xaraés. The treatment consisted of concentrate supplementation formulated to provide dietary 100% of RDP requirement (RDP100) or 150% of RDP requirement (RDP150). Increasing RDP over 50% of the requirement did not affect (P > 0.05) dry matter intake and digestibility. Rumen ammonia nitrogen, serum urea nitrogen and urine urea were higher (P < 0.05) in RDP150 than RDP100. However, no differences (P > 0.05) were observed between treatments for average daily gain or final body condition score. Increasing RDP above requirement does not improve intake, digestibility and performance of heifers in tropical pasture.