Effects of condensed tannin-enriched alternative energy feedstuff supplementation on performance, nitrogen utilization, and rumen microbial diversity in grazing beef cattle

•Condensed tannins are an efficient natural and organic compound to increase nitrogen use efficiency.•Pasture composition directly influences the supplementation strategy used and the response to the supplement.•Peanut skin is an efficient alternative supplement for pasture ruminant diets.•Alternative energy feedstuff supplementation increases animal performance and gain per area. This study aims to investigate the effects of alternative energy feedstuff supplementation containing condensed tannin (CT) on palisade grass pastures, focusing on intake, nutrient digestibility, animal performance, ruminal and blood parameters, nitrogen use efficiency (NUE), and its impacts on the ruminal bacterial community in backgrounding Nellore young bulls. Two experiments were conducted simultaneously. Animal performance was evaluated in Experiment 1. The experimental design was a completely randomized block; ninety Nellore bulls (Bos taurus indicus) with an average initial body weight (BW) of approximately 240 ± 5 kg were used (64 as testers and 26 as regulators). The feed intake, digestibility of dry matter and nutrients, ruminal parameters, NUE, and the impact on the ruminal bacterial community were evaluated in Experiment 2. The experimental design was a 4 × 4 double Latin square involving eight Nellore bulls with an average initial BW of 290 ± 8 kg, all of which were cannulated in the rumen. The treatments consisted of energy supplementation at 0.3 % of BW with peanut skin (PS), 0.3 % of BW with sorghum grain (SG), 0.3 % of BW with soybean hulls (SHs), and a control treatment with a supply of mineral salt ad libitum. The total digestible nutrient intake was lower in animals that received only mineral supplements (p < 0.005). The dry matter (DM) intake decreased with treatment PS, while the DM and nutrient digestibility increased (p < 0.005). There was a reduction in ruminal ammonia nitrogen and an improvement in NUE in the PS treatment (p < 0.005). However, the bacterial and Archaea populations were unaffected (p = 0.619). Individual animal performance and gain per kg were increased in the treatment with supplements containing or without CT compared to the mineral supplement (p < 0.001). The NUE improved in treatments PS, SG, and SH (p < 0.01). Feedstuff supplementation using no edible foods by products containing CTs is an effective alternative energy source for Nellore bulls grazing on palisade grass during the rainy season. Additionally, it can be used to mitigate