Impacts of different high-forage backgrounding lengths on the performance of early-maturing Nellore bulls, and effects of different concentrate levels in AGRI-002E sorghum silage- based diets on the metabolism of beef cattle
Authors:   , Pucetti Pauliane 
Published: September 2024

Our objectives with this study were 1) to evaluate the effects of implementing different high- forage backgrounding (HFB) in early-maturing Nellore bulls as an alternative strategy to conventional early mature bulls’ system, and 2) 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. For the first objective, forty young Nellore bulls, with an initial body weight (BW) of 265.25 ± 5 kg and an average age of 7 ± 1 month were used. The bulls were randomly allotted to four treatment groups with different HFB lengths (0, 28, 56, and 84 days), followed by a 14-day step-up adaptation period, and a high- concentrate finishing phase (140, 112, 84, and 56 days respectively). The HFB diet consisted of 800 g/kg of sorghum silage and 200 g/kg of concentrate, while the finishing diet contained 200 g/kg of corn silage and 800 g/kg of concentrate. Two digestibility trials were conducted for each treatment to estimate apparent digestibilities in both HFB and finishing phases. Bulls were weighed at the beginning and end of each phase to measure shrunk BW (SBW) and average daily gains (ADG). At the end of the experiment, all bulls were slaughtered to evaluate carcass characteristics. For the second objective, five rumen-cannulated Nellore bulls received five dietary treatments in a 5×5 Latin square experimental design, with diets containing 0, 200, 400, 600, and 800 g of concentrate/kg on a DM basis. Each period lasted 24 days, with 17 days for dietary adaptation and 7 days for data collection. In situ degradability assays, total feces and urine collection, and omasal and ruminal digesta collection were performed to estimate nutrient intake, digestibility, N balance, and ruminal parameters. In the first study, HFB did not influence nutrient intake, apparent digestibility, or performance during the backgrounding phase. However, during the finishing phase, increased HFB length improved the apparent digestibility of dry matter (DM), organic matter (OM), crude protein (CP), and non-fiber carbohydrates (NFC). The final SBW, carcass weight, and carcass gain were highest in the 0- day HFB group and lowest in the 84-day HFB group. Hot and cold carcass dressings were similar among the 0, 28, and 56-day HFB groups but lower in the 84-day HFB group. In conclusion, implementing HFB improves nutrient digestibility but does not affect nutrient intake, ADG, or gain-to-feed ratio during the finishing phase. While HFB may lead to a decrease in overall performance, both 28 and 56-day HFB lengths yield similar results in SBW, carcass weight, and carcass gain, suggesting a compensatory mechanism. In the second study, increasing concentrate levels in SS-based diets led to linear increases in the intake of DM, OM, CP, and ether extract (EE), with neutral detergent fiber (NDF) and starch intake showing quadratic responses. Ruminal digestibility of DM, OM, and CP exhibited quadratic responses, while NDF digestibility decreased linearly. Apparent total-tract digestibility of DM, OM, and EE increased linearly, whereas NDF and CP digestibility decreased linearly. Increasing concentrate levels improved in situ ruminal degradation parameters and nitrogen utilization, with higher total volatile fatty acids and microbial protein synthesis efficiency. The findings indicate that AGRI-002E sorghum silage is effective as a fiber source for high-concentrate diets, but its effectiveness is limited without concentrate supplementation. Keywords: Rearing phase, Nellore bulls, Concentrate levels, Roughage, Microbial protein synthesis, Total digestible nutrients.PUCETTI, Pauliane, D.Sc., Universidade Federal de Viçosa, março de 2024. Impactos de diferentes tempos de recria no desempenho de novilhos Nelore super precoces, e efeitos de diferentes níveis de concentrado em dietas à base de silagem de sorgo AGRI-002E no metabolismo de bovinos de corte