Two experiments were designed to evaluate the effects of monensin, virginiamycin, and flavomycin on growth performance, carcass characteristics, apparent total tract nutrient digestibility, and rumen fermentation of zebu cattle fed a no-roughage finishing diet (whole shelled corn [WSC] based). In Exp. 1, 100 crossbred bulls (; 392 kg [SD 46.8] average initial BW) were blocked by initial BW in a 101-d feedlot trial. Five treatments were evaluated using 4 pens per treatment (5 bulls/pen): monensin at 30 mg/kg DM, virginiamycin at 25 mg/kg DM, monensin at 20 mg/kg DM plus virginiamycin at 25 mg/kg DM, flavomycin at 4.4 mg/kg DM, and monensin at 20 mg/kg DM plus flavomycin at 2.2 mg/kg DM. There were no differences in growth performance (final BW, ADG, DMI, and G:F; ≥ 0.527) and carcass characteristics (HCW, dressing percent, and 12th-rib fat; ≥ 0.235) among treatments. In Exp. 2, 7 ruminally fistulated steers were used in a 7 × 7 Latin square design to evaluate the 5 treatments of Exp. 1 and 2 additional treatments: monensin at 30 mg/kg DM plus virginiamycin at 25 mg/kg DM and monensin at 20 mg/kg DM plus flavomycin at 4.4 mg/kg DM. Experimental periods were 14 d in length (9 d of adaptation and 5 d of measurements). Apparent total tract DM, OM, CP, and NDF digestibilities were similar among treatments ( ≥ 0.224). There was no treatment effect ( ≥ 0.253) in rumen fermentation responses (ruminal pH, rumen ammonia nitrogen, VFA, and number of protozoa). In conclusion, no evidence of benefits to cattle fed a no-roughage WSC-based diet was found to support the use of monensin combined with virginiamycin or flavomycin in the doses tested herein.

RESUMO -Objetivou-se com este estudo avaliar economicamente a terminação em confinamento de novilhos Red Angus superjovens alimentados até atingirem os pesos de abate pretendidos de 340, 370, 400 e 430 kg (pesos reais obtidos: 340, 373, 401 e 434 kg). O número de dias necessários para atingir os respectivos pesos foi de 114, 144, 168 e 209 dias aos 12, 13, 14 e 15 meses de idade. Os animais foram alimentados com dieta contendo 13,26% de PB e relação volumoso (silagem de milho):concentrado de 56,21:43,79 na MS. Na formação e condução da lavoura para produção de volumoso, as operações mais representativas do custo total/ha foram, em ordem decrescente, adubação de plantio (21,21%), adubação de cobertura (12,86%), sementes (11,40%) e controle de plantas daninhas (5,78%) e de pragas (4,52%). A alimentação (volumoso mais concentrado) foi o componente de custo mais representativo (média de 77,2%) se desconsiderado o custo de compra do animal. Da alimentação, o concentrado foi o componente mais oneroso (58,3%). O custo/kg de ganho de peso incrementou linearmente com o aumento no peso de abate, sendo de 1,94; 2,06; 2,15 e 2,34 R$/kg, respectivamente, para os pesos de abate de 340, 373, 401 e 434 kg. O incremento no peso de abate de 340 para 434 kg reduziu a lucratividade da terminação em confinamento de novilhos Red Angus superjovens.Palavras-chave: custo de alimentação, custo de produção, custo do confinamento, idade de abate, sistema de terminação Economic evaluation of feedlot finished Red Angus young steers slaughtered with different weightsABSTRACT -The objective of this experiment was to conduct an economic evaluation of feedlot finished Red Angus young steers fed to reach slaughter weights (SW) of 340, 370, 400 and 430 kg (actual SW of: 340, 373, 401 and 434 kg). Animals spent 114, 144, 168 and 209 days to reach the target SW at 12, 13, 14 and 15 months of age, respectively. Animals were fed a diet containing 13.26% crude protein and a forage (corn silage) to concentrate ratio of 56:44 (dry matter basis). The most representative operational costs (total costs/ha) for crop establishment and management were: crop fertilization (21.21%), top spreading fertilization (12.86%), seeds (11.40%), and weeds (5.78%) and insect control (4.52%). Feed (forage plus concentrate) represented 77.2% of the production cost when animal acquisition was not included in the calculation with concentrate accounting for 58.3% of these costs. The cost/kg of weight gain increased linearly from 1.94 to 2.34 R$/kg when SW was increased from 340 to 434 kg. Increasing SW from 340 to 434 kg reduced the profitability of feedlot finished Red Angus young steers.

-The objective of the present study was to evaluate the effects of dietary lipid content (20, 40 and 60 g/kg dry matter) on intake, total and ruminal apparent digestibility of dry matter (DM), nutrient digestibility, rumen fermentation parameters, microbial synthesis efficiency and rumen microbial content of beef cattle. Nine cannulated steers at 6 months of age with initial body weight of 232±35 kg were used in a triplicate 3 × 3 Latin square design. The results indicated that the total intake and digestibility of DM, organic matter (OM), gross energy (GE), neutral detergent fiber (NDF) and acid detergent fiber (ADF) were not affected by the lipid content of the diet. However, the lowest lipid content diet reduced the total digestibility of crude protein (CP) and total carbohydrate linearly compared with the highest lipid diet. In contrast, when steers were fed a diet containing 20 g lipids/kg of DM, the concentration of ammonia in the rumen decreased quadratically relative to the other diets. Ruminal pH was not affected by the interaction of treatment and sampling time; however, the rumen pH decreased quadratically in animals that received the highest dietary lipid content (60 g/kg) compared with animals that received 20 and 40 g lipids/kg of DM. The rumen concentrations of volatile fatty acids, propionate, and butyrate and the acetate/propionate ratio were affected by the dietary lipid content. However, the microbial population, microbial N flow, and efficiency of synthesis were not affected by dietary lipid content. Overall, an increase in the lipid content of the diet of Nellore steers resulted in similar digestive profiles and fermentation conditions.

This study was carried out to evaluate the effects of different nutritional strategies at growing and finishing phases on carcass and meat characteristics from 24 crossbred steers predominatly Holstein, slaughtered at 15 months of age and with 395.00kg of body weight. At the growing phase, the animals were maintained on Brachiaria brizantha pasture with two levels of supplementation in amounts equivalent to 0.5 or 1.0% of body weight. Subsequently, the animals were finished in feedlot with diets composed of 50 or 80% of concentrate. The high level of the concentrate at the finishing phase increased significantly (P<0.05) the hot carcass yield (50.16 vs. 48.62%). The lowest level of supplementation at the growing phase resulted in higher (P<0.05) percentage of carcass fat (25.61 vs. 23.39%) but it did not influence the percentage of muscle and bone. The high level of supplementation at the growing phase provided higher (p<0.05) meat tenderness, required less shear force (4.72 vs. 6.66kg cm-3) and lighter red meat (3.88 vs 2.89 points). The high feeding level during the growing phase was more interesting because it affected positively some important carcass and meat characteristics, especially tenderness.

Este artigo foi recebido em 15/12/2006 e aprovado em 12/8/2008. Correspondências devem ser enviadas para: ttberchi@fcav.unesp.br Revista Brasileira de Zootecnia © 2009 Sociedade Brasileira de Zootecnia ISSN 1516-3598 (impresso) ISSN 1806-9290 (on-line) www.sbz.org.br Influência do nitrogênio degradável no rúmen sobre a degradabilidade in situ, os parâmetros ruminais e a eficiência de síntese microbiana em novilhos alimentados com cana-de-açúcar 1 RESUMO -Objetivou-se avaliar o efeito da deficiência de nitrogênio degradável no rúmen (NDR), utilizando como volumoso cana-de-açúcar suplementada com uréia, farelo de soja ou farelo de glúten de milho -60, sobre a eficiência de síntese microbiana e a degradabilidade in situ da matéria seca (MS) e da fibra em detergente neutro (FDN) em novilhos mestiços. Utilizaram-se oito novilhos canulados no rúmen e duodeno, distribuídos em dois quadrados latinos 4 × 4 e alimentados com cana-de-açúcar e cana-de-açúcar suplementada com uréia, farelo de soja ou farelo de glúten de milho-60. O pH e a concentração de N-NH 3 foram mensurados no fluido ruminal antes e 2, 4, 6 e 8 horas após o fornecimento da ração. Utilizou-se a fibra em detergente ácido indigestível como indicador de fluxo duodenal. A eficiência microbiana foi determinada pelas bases purinas. As fontes de proteína degradável no rúmen não influenciaram a degradabilidade da matéria seca, entretanto, o maior valor de degradabilidade efetiva da FDN foi obtido com a cana-de-açúcar com farelo de soja. O pH e a concentração de N-NH 3 observados com todas as dietas foram adequados para o crescimento dos microrganismos ruminais. A deficiência de nitrogênio degradável no rúmen não influencia a síntese de proteína microbiana e a dinâmica de fase líquida. Palavras-chave: farelo de soja, glúten de milho-60, nitrogênio amoniacal, purinas, uréia Ruminal degradable nitrogen for steers fed sugar cane: in situ degradability, ruminal parameters and microbial synthesis efficiencyABSTRACT -The objective of this work was to evaluate the ruminal degradable nitrogen (RDN) deficit using as roughage sugar cane supplemented with urea, soybean meal, or corn gluten meal 60 on the microbial synthesis efficiency, in situ dry matter (DM) and neutral detergent fiber (NDF) degradability. The treatments were: sugar cane, sugar cane with urea, soybean meal or corn gluten meal 60. Eight rumen and duodenum cannulated steers were used and arranged according to two 4 × 4 Latin Squares. The pH and N-NH 3 were determined in the ruminal fluid before and 2, 4, 6 and 8 hours after feeding. The duodenal flow was estimated by indigestible acid detergent fiber. The microbial efficiency was determined by purine. RDN did not affect the DM and the highest effective degradability was observed in sugar cane supplemented with soybean meal in the NDF degradability. The pH, N-NH 3 values were appropriate to the microbial synthesis in all the evaluated diets. The RDN deficiency did not affect the microbial protein synthesis and the dynamics of the liquid phase.