Minimal dietary physical structure level for Belgian Blue double-muscled finishing bulls

The minimal amount of dietary physical structure for Belgian Blue double-muscled fattening bulls was investigated with four feeding regimens. The trial involved 52 bulls weighing 330 kg at the start and 680 kg at slaughter. All diets were fed ad libitum and consisted of concentrates and maize silage in different ratios. The structural value (SV), currently in use in Belgium as an index of dietary physical structure for dairy cattle, of the diets amounted to 0.79, 0.62 and 0.45 units per kg DM for the HSV (high), MSV (moderate) and LSV (low) group, respectively. The fourth group (LSVs) received the same diet as the LSV group, but additional straw was provided ad libitum, to evaluate whether bulls were capable of compensating for a possible lack of physical structure by eating straw. From the start until 600 kg no differences in growth rate were found. From 600 kg until slaughter (680 kg), the LSV group had the highest growth rate (1.35 vs. 1.14 kg.d(-1)). That same group also had the highest DM- and NEF-intake during the first 84 days of the trial. Although not significantly different, the MSV group had the highest amount of lean meat in the carcass (776 g.kg(-1)) and the lowest amount of fat (100 g.kg(-1)). The level of physical structure did not affect meat quality. Overall, no external signs of subclinical or clinical acidosis were observed. The length of the rumen papillae was not affected by the diets. Histological examination of the ruminal epithelium revealed that MSV and LSV exhibited the severest morphological changes. However, it is unclear whether the welfare of these animals was endangered by a shortage of physical structure. Based on the zootechnical performances, no adverse effects were found when feeding a diet with an SV of 0.45.kg(-1) DM.