PSXIV-9 Effect of fiber level on the performance of Nelore and ½ Angus-Nelore cattle.

Abstract Diets with high grain inclusion have become increasingly common in Brazilian feedlots. Data from our laboratory (Caetano et al., 2015) demonstrated that the feed intake of purebred Nelore cattle was maximized only at fiber levels above 11% neutral detergent fiber from forage (fNDF). These levels are higher than those observed for European breeds and those commonly used commercially, around 7% fNDF. Two experiments were conducted to evaluate fiber levels for confined Nelore and 1⁄2 Angus-Nelore cattle. The experiments were conducted under identical conditions for 50 days, assessing two levels of fNDF inclusion (12% and 7%) and the influence of breed and diet on animal performance. The first study involved 56 intact male Nelore cattle with an initial average weight of 460±38 kg and the second study used 60 intact male 1⁄2 Angus-Nelore cattle with an initial average weight of 398±10 kg. Both groups were evaluated in the same experimental feedlot, with the same diet, corn silage and management practices. The only forage source was corn silage with diets formulated to contain either 12% or 7% fNDF (equivalent to 23.3% or 13.6% silage in total dry matter). The treatments contained 64% and 73.5% ground corn and 0.2% and 0.5% potassium chloride, respectively, for the 12% and 7% fNDF diets. Additionally, both diets included soybean meal (1.5%), cottonseed (7%), urea (1.2%), a mineral mix (2.7%) and monensin (25 ppm) and were formulated to meet protein and mineral nutritional requirements according to the RLM model (rlm.app.br). Feed intake was monitored through real-time feeders (Growsafe) and weight gain was estimated by linear regression using live weights obtained from real-time scales at water troughs (Intergado). Statistical analyses were performed using a completely randomized design considering each animal as an experimental unit (SAS University, 2012). The 1⁄2 Angus-Nelore cattle showed higher weight gain with a significant interaction effect between diet and breed (P = 0.0023) (2.20 vs. 1.54 kg/day). The average daily dry matter intake was also higher in these animals compared to the Nelore ones with a diet-breed interaction (P = 0.0067) (11.71 vs. 10.49 kg/day). Moreover, the 1⁄2 Angus-Nelore cattle had better feed conversion with a diet-breed interaction effect (P = 0.0095) (5.43 vs. 7.07) and greater feed efficiency (P = 0.012) (0.188 vs. 0.146). It is concluded that breed had an impact on performance, with 1⁄2 Angus-Nelore cattle showing superiority in all evaluated variables compared to Nelore.