Effect of different degraded protein balances (OEB) on the performance of beef bulls and on digestibility and rumen fermentation in sheep

Abstract

One-hundred and twenty-five non-double-muscled Belgian Blue finishing bulls (live weight range 375-620 kg) were used to investigate the effect of different levels of degraded protein balance in the rumen (OEB; -2, -7, -16 and -22 g kg -1 dry matter; DM) on animal performance, with the dietary content of true protein digested in the small intestine (DVE) fixed at 80 g kg -1 . Lower OEB levels significantly reduced daily liveweight gain from 1.57 to 1.39 kg during the first 84 days of the experiment, but not during the subsequent part. For the whole experiment, daily liveweight gain decreased from 1.40 to 1.32 kg but the difference was not significant. Intake of DM, DVE and net energy for fattening was not modified by OEB level, while crude protein intake was reduced and OEB lack was increased. An OEB level of -22 g kg -1 DM resulted in a significantly unfavourable conversion of DM and net energy during the initial months (11.3 and 11.5% compared to OEB = -2 g kg -1 DM, respectively). For the total period the conversion of DM and net energy was still less favourable, but the differences were not significant. There was a nominal decrease in cold carcass weight and dressing proportion when OEB level decreased, but the effect was not significant. The effect of different OEB levels on digestibility and rumen fermentation was investigated in a separate experiment with wethers. Apparent protein digestibility was reduced from 74.2 to 68.9% when OEB level decreased. Rumen pH and concentrations and molar percentages of volatile fatty acids were not altered by OEB level. Ammonia concentration was only reduced by a lower OEB level at 7 hr after feeding. Because of a nominal reduction in daily liveweight gain, feed efficiency, carcass weight, dressing percentage and carcass conformation with decreasing OEB level, it is advisable not to feed less than -16 g OEB kg -1 DM in diets with 80 g DVE kg -1 DM to Belgian Blue nondouble-muscled finishing bulls from 375 kg onwards. This tolerable OEB lack is larger than proposed in case of protein overfeeding.