Effects of different concentrate levels in AGRI-002E sorghum silage-based diets on nutrient intake and digestibility, ruminal pH and ammonia concentration, ruminal degradability, and microbial efficiency in beef cattle

Abstract

This study aimed to evaluate the effect of increasing concentrate levels in AGRI-002E sorghum silage (SS)-based diets on nutrient intake and digestibility, ruminal pH and ammonia concentration, Nitrogen (N) balance, efficiency of microbial protein synthesis, and in situ degradability of complete diets. Five rumen-cannulated Nellore bulls (age = 8 ± 1.0 months; initial BW = 242 ± 5 kg) received five dietary treatments in a 5×5 Latin square experimental design. The dietary treatments consisted of five concentrate levels (0, 200, 400, 600, and 800 g of concentrate/kg on a DM basis) in SS-based diets. The experiment lasted 120 d, with five periods of 24 d. Each period consisted of 17 d for dietary adaptation, and 7 d for data collection. In situ degradability assays were conducted to estimate ruminal degradability. Total feces and urine collection were performed to estimate nutrient intake and digestibility and estimate N balance. Omasal and ruminal digesta collection were performed to estimate ruminal digestibility and ruminal parameters. Increasing concentrate levels in SS-based diets led to linear increases (P<0.001) in the intake of dry matter (DM), organic matter (OM), crude protein (CP), and ether extract (EE). Neutral detergent fiber corrected for ash and protein contamination (apNDF) and starch intake showed quadratic responses (P≤0.008). Ruminal digestibility of DM, OM and CP responded quadratically (P≤0.040), while apNDF exhibited linear decrease (P=0.003). Starch ruminal digestibility exhibited a cubic effect (P=0.016). Apparent total-tract digestibility of DM, OM, and EE increased linearly (P≤0.001), whereas apNDF, and CP digestibility decreased linearly (P≤0.012), and starch presented a quadratic effect (P=0.029). In situ ruminal degradation parameters increased linearly with higher concentrate levels (P<0.001). Ruminal pH exhibited a quadratic pattern (P=0.006), ammonia concentration linearly decreased (P=0.003). Total volatile fatty acids, and butyrate showed linear increases (P<0.001), acetate and propionate had quadratic effects (P<0.001), while the ratio Acetate to Propionate decreased linearly (P<0.001). N intake, fecal N excretion, retained N, total digestible nutrients, digestible organic matter, and microbial production increased linearly (P<0.001), although urine N excretion, urinary urea, and blood urea concentration decreased linearly (P<0.028). Therefore, increasing concentrate levels in AGRI-002E sorghum silage-based diets improve TDN intake, microbial protein synthesis efficiency, in situ ruminal degradability parameters, and nitrogen utilization. Moreover, our findings indicate that AGRI-002E sorghum silage demonstrates potential as a fiber source for high-concentrate diets. However, its effectiveness is limited without concentrate supplementation, emphasizing the importance of balanced dietary composition for optimal utilization in beef cattle.