RESUMO
The energy content of finishing diets offered to feedlot cattle may vary across countries. We assumed that the lower is the energy content of the finishing diet, the shorter can be the adaptation period to high-concentrate diets without negatively impacting rumen health while still improving feedlot performance. This study was designed to determine the effects of adaptation periods of 6, 9, 14 and 21 days on feedlot performance, feeding behaviour, blood gas profile, carcass characteristics and rumen morphometrics of Nellore cattle. The experiment was designed as a completely randomised block, replicated 6 times, in which 96 20-month-old yearling Nellore bulls (391.1 ± 30.9 kg) were fed in 24 pens (4 animals/pen) according to the adaptation period adopted: 6, 9, 14 or 21 days. The adaptation diets contained 70%, 75% and 80.5% concentrate, and the finishing diet contained 86% concentrate. After adaptation, one animal per pen was slaughtered (n = 24) for rumen morphometric evaluations and the remaining 72 animals were harvested after 88 days on feed. Orthogonal contrasts were used to assess linear, quadratic and cubic relationships between days of adaptation and the dependent variable. Overall, as days of adaptation increased, final BW (P = 0.06), average daily gain (ADG) (P = 0.07), hot carcass weight (P = 0.04) and gain to feed ratio (G : F) (P = 0.07) were affected quadratically, in which yearling bulls adapted by 14 days presented greater final BW, ADG, hot carcass weight and improved G : F. No significant (P > 0.10) days of adaptation effect was observed for any of feeding behaviour variables. As days of adaptation increased, the absorptive surface area of the rumen was affected cubically, where yearling bulls adapted by 14 days presented greater absorptive surface area (P = 0.03). Thus, Nellore yearling bulls should be adapted by 14 days because it led to improved feedlot performance and greater development of rumen epithelium without increasing rumenitis scores.
Assuntos
Ração Animal , Bovinos/fisiologia , Rúmen , Adaptação Fisiológica , Ração Animal/análise , Animais , Dieta/veterinária , Comportamento Alimentar , MasculinoRESUMO
This 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.