Given the barriers in the degradability of the fibrous fraction of feed, two experiments were conducted with the objective of evaluating the use of fibrolytic enzymes (EFE) with xylanase and cellulase activities in feedlot diets for beef cattle, originating this dissertation. In the first experiment, the objective of the study was to determine the effect of the fibrolytic enzyme in the diet of finishing feedlot Nellore bulls with diets containing two sources and two levels of roughage inclusion. Two hundred and sixty-four Nellore bulls (371 ± 18.7 kg) were distributed in 48 pens by initial BW in a randomized complete block design with a 2 × 2 × 2 factorial arrangement of treatments. The finishing period was 95 days and diets were composed, on DM basis, of EFE or not (0.75 ml/kg DM; ABVista, Marlborough, UK), 8.5 or 12.5% of sugarcane bagasse (SCB) or grass hay (GH), 59 or 55% of ground corn, 15% of corn gluten feed, 15% of soybean hulls, 1.5% of minerals and vittamins with monensin, and 1% of urea. Animal performance was not significantly affected by the addition of EFE (P>0.10). Dry matter intake was higher for treatments with 12.5% of roughage (P<0,01) and for treatments with GH (P=0,01), but G:F was higher for 8.5% of roughage (P<0,01) and tended to be higher for SCB (P=0,07). Observed net energy concentrations were higher for 8.5% of roughage inclusion (P<0,01) and for SCB (P=0,04). In the second experiment, the objective was to evaluate ruminal parameters, total tract digestibility, and feeding behavior of 8 Nellore steers (396 ± 1.4 kg) receiving the same diets that the performance trial. The steers were assigned to two independent 4 × 4 Latin Squares (LSQ) with a 2 × 2 factorial arrangement of treatments, in which each LSQ received one different source of roughage. For steers fed SCB, digestibility of nutrients were not affected by the level o roughage nor by the presence of EFE (P>0.10). For steers fed GH the digestibility of CP was higher for 8.5% than for 12.5% of dietary roughage (P=0.01). The supplementation of EFE tended to increase the digestibilities of DM (P=0.08) and of CP (P=0.06) of GH diets. For animals fed SCB the molar proportion of isovalerate (P<0.01) was lower with 12.5% of dietary roughage and there was a tendency of reduction on total VFA concentration (P=0.06) and on molar proportion of valerate (P=0.07) compared to 8.5% of SCB. The EFE supplementation tended to increase the molar proportion of isovalerate (P=0.09) for SCB diets. In GH treatments, the acetate:propionate ratio was lower with the inclusion of 8.5% of roughage (P=0.04). The EFE supplementation tended to decrease the molar proportion of propionate (P=0.06), and increased the acetate:propionate ratio (P=0.03) and the molar proportions of isobutyrate and isovalerate (P<0.01). To conclude, the EFE supplementation do not improve the performance of feedlot cattle fed diets containing SCB or GH, but result in some positive effects on digestibility and in some effects on ruminal parameters of animals fed GH. The inclusion of 12.5% of SCB or GH in diets of feedlot cattle containing ground flint corn, soybean hulls, and corn gluten feed increase DMI, but decrease G:F compared to the inclusion of 8.5% of these sources of roughage. On level of inclusion of 8.5 or 12.5% of DM, SCB reduces DMI, with no alteration on ADG, and consequently improves G:F of feedlot cattle containing ground flint corn, soybean hulls, and corn gluten feed. / Haja vista as barreiras na degradabilidade da fração fibrosa dos alimentos, dois experimentos foram conduzidos com o objetivo de avaliar o uso de enzimas fibrolíticas exógenas (EFE) com atividades de xylanase e celulase em dietas de confinamento para gado de corte, dando origem a um capítulo desta dissertação. No primeiro experimento, o objetivo foi determinar o efeito da enzima fibrolítica na dieta de machos inteiros da raça Nelore terminados em confinamento com dietas contendo duas fontes e dois níveis de volumoso. Duzentos e sessenta e quatro animais foram distribuídos em 48 baias pelo peso vivo inicial (371 ± 18,7) em um delineamento em blocos casualizados com arranjo fatorial 2 × 2 × 2. O período de terminação foi de 95 dias e as dietas continham, na base seca, EFE ou não (0,75 ml/kg de MS; ABVista, Marlborough, UK), 8,5 ou 12,5% de bagaço-de-cana-de-açúcar (SCB) ou de feno de gramínea (GH), 59 ou 55% de milho moído, 15% de farelo proteinoso de milho (corn gluten feed), 15% de casca de soja, 1,5% de minerais e vitaminas com monensina e 1% de ureia. A adição de EFE não afetou significativamente os dados de desempenho animal (P>0,10). O CMS foi maior para as dietas com 12,5% de volumoso (P<0,01) e para as dietas com feno (P=0,01), mas a EA (GPD/CMS) foi maior com 8,5% de volumoso (P<0,01) e tendeu a ser maior com SCB (P=0,07). As energias líquidas para a manutenção (ELm) e para o ganho (ELg) observadas foram maiores para o nível de inclusão de 8,5% (P<0,01) e para o SCB (P=0,04). No segundo experimento, o objetivo foi avaliar parâmetros ruminais, digestibilidade do trato digestivo total e comportamento alimentar de oito novilhos Nelore (396 ± 1,4 kg) recebendo as mesmas dietas que no experimento de desempenho. Os novilhos foram designados a dois Quadrados Latinos (LSQ) 4 × 4 independentes com arranjo fatorial 2 × 2, em que cada LSQ recebeu uma fonte de volumoso diferente. Para os bovinos alimentados com SCB, a digestibilidade dos nutrientes não foi afetada pelo nível de volumoso nem pela presença de EFE (P>0,10). Para os animais alimentados com GH a digestibilidade da PB foi maior com 8,5% do que com 12,5% de volumoso na dieta (P=0,01). A suplementação com EFE tendeu a aumentar as digestibilidades da MS (P=0,08) e da PB (P=0,06) das dietas com GH. Para os animais alimentados com SCB a proporção molar de isovalerato (P<0,01) foi menor com 12,5% de volumoso na dieta e houve tendência de redução na concentração total de AGV (P=0.06) e na proporção molar de valerato (P=0,07) em comparação com 8,5% de SCB. A suplementação com EFE tendeu a aumentar a proporção molar de isovalerato (P=0,09) para dietas com SCB. Nos tratamentos com GH, a relação acetato:propionato foi menor com a inclusão de 8,5% de volumoso (P=0,04). A suplementação com EFE tendeu a diminuir a proporção molar de propionato (P=0,06) e aumentou a relação acetato:propionato (P=0,03) e as proporções molares de isobutirato e isovalerto (P<0,01). Concluindo, a suplementação com EFE não melhora o desempenho de bovinos confinados com dietas contendo SCB ou GH, mas resulta em alguns efeitos positivos na digestibilidade e altera alguns parâmetros ruminais de animais alimentados com GH. A inclusão de 12,5% de SCB ou GH na dieta de bovinos confinados contendo milho flint moído, casca de soja e farelo proteinoso de milho, aumenta o CMS, mas diminui a EA comparada com a inclusão de 8,5% dessas fontes de volumoso. Nos níveis de inclusão de 8,5 ou 12.5% da MS da dieta, o SCB reduz o CMS, sem alteração no GPD e consequentemente melhora a EA de bovinos confinados com dietas contendo milho flint moído, casca de soja e farelo proteinoso de milho.

Given the barriers in the degradability of the fibrous fraction of feed, two experiments were conducted with the objective of evaluating the use of fibrolytic enzymes (EFE) with xylanase and cellulase activities in feedlot diets for beef cattle, originating this dissertation. In the first experiment, the objective of the study was to determine the effect of the fibrolytic enzyme in the diet of finishing feedlot Nellore bulls with diets containing two sources and two levels of roughage inclusion. Two hundred and sixty-four Nellore bulls (371 ± 18.7 kg) were distributed in 48 pens by initial BW in a randomized complete block design with a 2 × 2 × 2 factorial arrangement of treatments. The finishing period was 95 days and diets were composed, on DM basis, of EFE or not (0.75 ml/kg DM; ABVista, Marlborough, UK), 8.5 or 12.5% of sugarcane bagasse (SCB) or grass hay (GH), 59 or 55% of ground corn, 15% of corn gluten feed, 15% of soybean hulls, 1.5% of minerals and vittamins with monensin, and 1% of urea. Animal performance was not significantly affected by the addition of EFE (P>0.10). Dry matter intake was higher for treatments with 12.5% of roughage (P<0,01) and for treatments with GH (P=0,01), but G:F was higher for 8.5% of roughage (P<0,01) and tended to be higher for SCB (P=0,07). Observed net energy concentrations were higher for 8.5% of roughage inclusion (P<0,01) and for SCB (P=0,04). In the second experiment, the objective was to evaluate ruminal parameters, total tract digestibility, and feeding behavior of 8 Nellore steers (396 ± 1.4 kg) receiving the same diets that the performance trial. The steers were assigned to two independent 4 × 4 Latin Squares (LSQ) with a 2 × 2 factorial arrangement of treatments, in which each LSQ received one different source of roughage. For steers fed SCB, digestibility of nutrients were not affected by the level o roughage nor by the presence of EFE (P>0.10). For steers fed GH the digestibility of CP was higher for 8.5% than for 12.5% of dietary roughage (P=0.01). The supplementation of EFE tended to increase the digestibilities of DM (P=0.08) and of CP (P=0.06) of GH diets. For animals fed SCB the molar proportion of isovalerate (P<0.01) was lower with 12.5% of dietary roughage and there was a tendency of reduction on total VFA concentration (P=0.06) and on molar proportion of valerate (P=0.07) compared to 8.5% of SCB. The EFE supplementation tended to increase the molar proportion of isovalerate (P=0.09) for SCB diets. In GH treatments, the acetate:propionate ratio was lower with the inclusion of 8.5% of roughage (P=0.04). The EFE supplementation tended to decrease the molar proportion of propionate (P=0.06), and increased the acetate:propionate ratio (P=0.03) and the molar proportions of isobutyrate and isovalerate (P<0.01). To conclude, the EFE supplementation do not improve the performance of feedlot cattle fed diets containing SCB or GH, but result in some positive effects on digestibility and in some effects on ruminal parameters of animals fed GH. The inclusion of 12.5% of SCB or GH in diets of feedlot cattle containing ground flint corn, soybean hulls, and corn gluten feed increase DMI, but decrease G:F compared to the inclusion of 8.5% of these sources of roughage. On level of inclusion of 8.5 or 12.5% of DM, SCB reduces DMI, with no alteration on ADG, and consequently improves G:F of feedlot cattle containing ground flint corn, soybean hulls, and corn gluten feed. / Haja vista as barreiras na degradabilidade da fração fibrosa dos alimentos, dois experimentos foram conduzidos com o objetivo de avaliar o uso de enzimas fibrolíticas exógenas (EFE) com atividades de xylanase e celulase em dietas de confinamento para gado de corte, dando origem a um capítulo desta dissertação. No primeiro experimento, o objetivo foi determinar o efeito da enzima fibrolítica na dieta de machos inteiros da raça Nelore terminados em confinamento com dietas contendo duas fontes e dois níveis de volumoso. Duzentos e sessenta e quatro animais foram distribuídos em 48 baias pelo peso vivo inicial (371 ± 18,7) em um delineamento em blocos casualizados com arranjo fatorial 2 × 2 × 2. O período de terminação foi de 95 dias e as dietas continham, na base seca, EFE ou não (0,75 ml/kg de MS; ABVista, Marlborough, UK), 8,5 ou 12,5% de bagaço-de-cana-de-açúcar (SCB) ou de feno de gramínea (GH), 59 ou 55% de milho moído, 15% de farelo proteinoso de milho (corn gluten feed), 15% de casca de soja, 1,5% de minerais e vitaminas com monensina e 1% de ureia. A adição de EFE não afetou significativamente os dados de desempenho animal (P>0,10). O CMS foi maior para as dietas com 12,5% de volumoso (P<0,01) e para as dietas com feno (P=0,01), mas a EA (GPD/CMS) foi maior com 8,5% de volumoso (P<0,01) e tendeu a ser maior com SCB (P=0,07). As energias líquidas para a manutenção (ELm) e para o ganho (ELg) observadas foram maiores para o nível de inclusão de 8,5% (P<0,01) e para o SCB (P=0,04). No segundo experimento, o objetivo foi avaliar parâmetros ruminais, digestibilidade do trato digestivo total e comportamento alimentar de oito novilhos Nelore (396 ± 1,4 kg) recebendo as mesmas dietas que no experimento de desempenho. Os novilhos foram designados a dois Quadrados Latinos (LSQ) 4 × 4 independentes com arranjo fatorial 2 × 2, em que cada LSQ recebeu uma fonte de volumoso diferente. Para os bovinos alimentados com SCB, a digestibilidade dos nutrientes não foi afetada pelo nível de volumoso nem pela presença de EFE (P>0,10). Para os animais alimentados com GH a digestibilidade da PB foi maior com 8,5% do que com 12,5% de volumoso na dieta (P=0,01). A suplementação com EFE tendeu a aumentar as digestibilidades da MS (P=0,08) e da PB (P=0,06) das dietas com GH. Para os animais alimentados com SCB a proporção molar de isovalerato (P<0,01) foi menor com 12,5% de volumoso na dieta e houve tendência de redução na concentração total de AGV (P=0.06) e na proporção molar de valerato (P=0,07) em comparação com 8,5% de SCB. A suplementação com EFE tendeu a aumentar a proporção molar de isovalerato (P=0,09) para dietas com SCB. Nos tratamentos com GH, a relação acetato:propionato foi menor com a inclusão de 8,5% de volumoso (P=0,04). A suplementação com EFE tendeu a diminuir a proporção molar de propionato (P=0,06) e aumentou a relação acetato:propionato (P=0,03) e as proporções molares de isobutirato e isovalerto (P<0,01). Concluindo, a suplementação com EFE não melhora o desempenho de bovinos confinados com dietas contendo SCB ou GH, mas resulta em alguns efeitos positivos na digestibilidade e altera alguns parâmetros ruminais de animais alimentados com GH. A inclusão de 12,5% de SCB ou GH na dieta de bovinos confinados contendo milho flint moído, casca de soja e farelo proteinoso de milho, aumenta o CMS, mas diminui a EA comparada com a inclusão de 8,5% dessas fontes de volumoso. Nos níveis de inclusão de 8,5 ou 12.5% da MS da dieta, o SCB reduz o CMS, sem alteração no GPD e consequentemente melhora a EA de bovinos confinados com dietas contendo milho flint moído, casca de soja e farelo proteinoso de milho.

A high moisture corn/soybean meal-based finishing ration was used to examine the effects of roughage source (corn silage, alfalfa hay), level of dietary roughage (8, 16, 24%), and ractopamine supplementation (none, Optaflexx) on growth performance, carcass traits, and beef quality for finishing 108 steers and 24 heifers (initial BW = 308 kg). Cattle were allocated by gender to 12 management regimen subclasses. Optaflexx (trade name for ractopamine hydrochloride) was fed over the last 28 d on feed with cattle marketed after common days on feed. Growth performance (ADG, feed intake, and feed efficiency) and carcass traits were assessed on an individual animal basis. A primal rib and semitendinosus (ST) muscle from each animal were processed at the University of Guelph Meat Laboratory for carcass and meat quality evaluations. Tenderness was determined using shear force assessment of product aged 7, 14, and 21 d. Average daily gains were similar (P > 0.27) across main effects while use of corn silage as the roughage source decreased (P < 0.001) dry matter intake and improved (P < 0.001) feed efficiency compared to feeding alfalfa hay. Roughage level and beta agonist supplementation did not affect (P > 0.13) dry matter intake or feed efficiency. When the last 28 days on feed were examined, Optaflexx supplementation increased (P < 0.001) weight change, ADG, and improved feed conversion, while DMI remained unchanged (P > 0.373). Carcass traits including hot carcass weight, grade fat, longissimus muscle area, marbling, and body composition as assessed by rib dissection (% lean, fat, bone) were not affected (P > 0.14) by roughage level, source, or use of Optaflexx. Fat partitioning and liver abscess scores were unaffected (P > 0.09) by source and level of roughage fed, and use of Optaflexx. Source and level of dietary roughage did not affect color (P > 0.21) or shear force (P > 0.20) values for longissimus (LM) and semitendinosus (ST) steaks. Lower DMI and better feed conversion can be achieved using corn silage as the roughage source, while inclusion of up to 24% roughage in finishing diets may not negatively impact gains, carcass characteristics or beef quality. Beef producers may be able to increase amounts of roughage in the diet to lower cost of production without compromising growth performance and carcass and meat quality.