ABSTRACT The objectives were to evaluate the effects of monensin and virginiamycin, alone or combined, on supplemented Nellore cattle grazing tropical grass during the rainy season. Two experiments were conducted simultaneously to evaluate intake, digestibility, CH4 emissions, blood parameters, performance, and carcass characteristics (Exp. 1), and ruminal fermentation and relative abundance of ruminal microorganisms (Exp. 2). Animals (n = 92 Exp. 1 and n = 12 Exp. 2) were distributed in a completely randomized design and allocated in twelve paddocks composed of Urochloa brizantha (A. Rich.) Stapf. cv. Xaraés. A protein-energetic supplementation of 3 g/kg of BW per day was provided to all animals. Supplements were: without additives (WA), monensin alone at 80 mg/kg of product (MN), virginiamycin alone at 150 mg/kg of product (VM), and monensin (80 mg/kg of product) combined with virginiamycin (150 mg/kg of product; MNVM). Treatments did not affect intakes of total dry matter (DM), supplement DM, and nutrients. However, the intakes of forage DM and crude protein decreased in cattle fed MNVM compared with animals fed WA, MN, and VM. Total volatile fatty acids increased in animals fed VM. Ruminal NH3-N decreased, and pH increased in animals fed MN, VM, and MNVM. Relative abundance of total F. succinogenes and S. ruminantium decreased and R. flavefaciens increased in animals fed MN and VM at d 118. Treatments had no effect on enteric CH4 emissions. The average daily gain (ADG) and total gain were greater in cattle fed MNVM than in cattle fed MN. Combination of monensin and virginiamycin altered the rumen microbial populations but did not decrease enteric CH4 emissions. However, it decreased forage dry matter intake without altering the ADG and total weight gain, leading to an increase in feed efficiency. Results from this study indicate an advantage in including feed additives combined in the diet of supplemented Nellore cattle grazing tropical grass during the rainy season.

Neste estudo foi avaliado o efeito da substituição parcial do milho pela glicerina e óleos essenciais (Essential®) na dieta de bovinos da raça Nelore terminados em confinamento Trinta touros com peso médio de 400 ± 34,1 kg foram alojados em baias coletivas (10 x 20 m²) por 63 dias. Os touros foram divididos aleatoriamente em três dietas (10 touros por tratamento): CON - controle (sem glicerina ou óleos essenciais); GLI - Glicerina (15% na matéria seca - MS) e GEO - Glicerina (15% na MS) e Essential® (óleo de caju líquido e mamona, 3 g animal dia-1). Três marcadores diferentes foram utilizados para estimar a digestibilidade aparente das dietas: matéria seca indigestível - MSi, fibra em detergente neutro indigestível - FDNi e lignina purificada - LIPE®. A substituição do milho pela glicerina e adição de Essential® nas dietas aumentou a digestibilidade da MS e matéria orgânica para os animais. A inclusão de glicerina na dieta reduziu a digestibilidade aparente da FDN, carboidratos fibrosos e não fibrosos. Os marcadores das iDM , FDNi e LIPE® estimaram de forma semelhante a digestibilidade aparente de todos os nutrientes de todas as dietas experimentais.

Current research studied the effect of partial replacing corn by glycerin and essential oils addition in the diet of Nellore bulls finished in feedlot. Thirty bulls with average weight 400 ± 34.1 kg were housed in collective pens (10 x 20 m²) for 63 days. The bulls were randomly assigned to 3 diets (10 bulls per treatment): CON - Control (without glycerin or Essential® oils); GLY - Glycerin (15% on dry matter - DM); and GEO - Glycerin (15% on DM) and Essential® oils (3 g animal day-1). Three different markers were used to estimate apparent digestibility in the diets: indigestible dry matter - iDM; indigestible neutral detergent fiber - iNDF; and purified lignin - LIPE®. Feed efficiency and animal performance were not affected by the corn partial replacing by glycerin. Partial corn replacing by glycerin and Essential® oils addition in the diets increased the DM and organic matter apparent digestibility for bulls. The glycerin addition in the diet decreased NDF, fibrous carbohydrate and non-fibrous carbohydrate digestibility. Apparent digestibility estimated by markers iDM, iNDF and LIPE® were similar to all nutrients in the diet.