Effect of the rumen-degradable to rumen-undegradable protein ratio and roughage type in diets for steers

The objective was to evaluate the effects of the rumen-degradable protein (RDP) to rumen-undegradable protein (RUP) ratio and two roughage types on intake, digestibility, nitrogen utilization efficiency, and microbial protein synthesis in cattle. Four Jersey steers (initial average age of 18 months and initial average body weight of 316,8 ± 4,0 kg) were assigned to a 4 × 4 Latin square design with a 2 × 2 factorial arrangement. Factor 1 was roughage type [Tifton hay or ryegrass haylage], and Factor 2 was the RDP:RUP ratio [low ratio (LR) = 60:40; high ratio (HR) = 65:35], based on crude protein (%). Steers fed Tifton hay exhibited greater intake of dry matter (7,45 kg), organic matter (7,25 kg), and non-fiber carbohydrates (2,66 kg; P < 0.05). Ammonia and amino acid concentrations were higher in steers fed Tifton hay (10,75 and 44,98 mg/dL, respectively) than steers fed ryegrass haylage. The high RDP:RUP ratio resulted in increased sugar concentrations. The RDP:RUP ratios evaluated did not influence any of the overall outcomes; therefore, it can be concluded that both RDP:RUP ratios are suitable for use in diets containing either tropical or temperate grasses.