SummaryThis study was designed to determine effects of quantitatively restricted intake of the final finishing diet as a means of dietary adaptation compared with diets increasing in concentrate (step up) over periods of 6 and 9 days on feedlot performance, carcass characteristics, feeding behaviour, blood gas profile and rumen morphometrics of Nellore cattle. One hundred twenty 22-month-old Nellore bulls (352 ± 20 kg) were randomly allocated in 24 pens and fed for 84 days. The experimental design was a completely randomized block with 2 × 2 factorial arrangement of treatments: adaptation using either step up protocol for 6 days or 9 days or restriction protocol for 6 days or 9 days, where the pen (five bullocks/pen; six pens/treatment) was considered the experimental unit. Cattle adapted by step up protocol had significantly greater average daily gain throughout the study when compared to those adapted by restriction protocol, regardless of adaptation length. During the adaptation period, a greater dry matter intake fluctuation was observed for animals maintained on restriction programme when compared to those adapted to the finishing diets using step up protocol. In addition, a protocol × length interaction for rumenitis scores was observed, where the level of injuries to the ruminal wall was significantly higher for the cattle adapted by restriction protocol for 9 days and lower for animals submitted for 9 days to the step up programme. Likewise, a protocol × length interaction for mitotic index was observed, in which cattle adapted by step up protocol for 9 days had lower numbers of cells in mitosis. Thus, the step up protocol led to better feedlot performance, and based on this fact, the length of 9 days promoted better rumen epithelium adaptation of Nellore cattle to high-concentrate diets. K E Y W O R D Sconcentrate, intake, papillae, protocol, rumen

The experiment was designed to determine the effects of different doses of sodium monensin (MON) on rumen papillae and tissue histology of feedlot Nellore cattle. The experiment was designed as a completely randomised block, replicated 12 times, in which 60 20-month-old yearling Nellore bulls (402.52 ± 33.0 kg) were fed in individual pens for 84 days according to the following doses of MON expressed in ppm (on a dry-matter basis): 0, 9, 18, 27 and 36. The adaptation program consisted of ad libitum feeding of two adaptation diets over a period of 14 days, with concentrate level increasing from 68% to 84% of diet dry matter. Orthogonal contrasts were used to assess linear, quadratic, cubic and quartic relationships between doses of MON and the dependent variable. No significant (P > 0.10) MON effect was observed for number of papillae, mean papillae area, papillae area as a percentage of absorptive surface and rumenitis incidence. However, as the dose of MON increased, the absorptive surface area, papillae surface area and mitotic index were affected (P < 0.05) cubically, in which animals fed 9 and 36 ppm presented larger absorptive surface area and greater number of cells in mitosis. Thus, based on the results, feeding of MON affected rumen papillae and tissue histology of feedlot Nellore cattle. The doses of 9 or 36 ppm of MON should be considered as the most feasible options, because they promote better development of rumen epithelium.

O objetivo com este estudo foi avaliar o efeito do probiótico a base de bactérias produtoras de lactato (DBR) e da monensina sódica (MON) sobre o desempenho produtivo e características de carcaça de bovinos Nelore terminados em confinamento. Foram utilizados 18 machos, não castrados, com média de idade de 18 meses e 362,0 ±30,0kg de peso vivo inicial, divididos em três tratamentos: 1) 2g de DBR; 2) 1g de DBR + 138mg de MON e; 3) 275mg de MON, caracterizando delineamento inteiramente casualizado, com 6 animais por tratamento, divididos em 18 baias (1 animal/baia) em sistema de alimentação do tipo Calan Gate. O experimento teve duração de 84 dias, os animais foram pesados e submetidos a avaliações de ultrassonografia a cada 28 dias. Não houve efeito dos aditivos alimentares em relação ao peso vivo final e consumo de massa seca em percentagem do peso vivo. O ganho de peso diário foi menor nos primeiros 28 e 56 dias de estudo para animais que consumiram MON e DBR+MON, porém não foram observadas diferenças entre os tratamentos no período total. Animais alimentados com DBR+MON apresentaram maior consumo de massa seca durante todo o estudo, porém pior conversão alimentar que aqueles alimentados com DBR ou MON. Animais alimentados com DBR+MON apresentaram menor rendimento de carcaça que aqueles suplementados com DBR apenas e animais suplementados com MON tiveram maior espessura de gordura subcutânea ao final do estudo. A suplementação com o DBR apenas, pode ser uma alternativa para substituir a monensina.