Effects of physically effective neutral detergent fibre content on dry-matter intake, digestibility and chewing activity in beef cattle fed total mixed ration

Our aim in this study was to determine the effects of physically effective neutral detergent fibre (peNDF) in a total mixed ration (TMR) on feed intake, digestibility and chewing activity in beef cattle. The experiment had a replicated 3 × 3 Latin square desig, using three fattening Hanwoo (Bos taurus coreanae) steers with ruminal cannulas. Steers were offered one of three diets (high, medium or low peNDF content) obtained by mixing the same TMR for different periods of time (5, 13 and 25 min). peNDF content of TMR was calculated as [total chewing time/NDF intake (kg)] × dietary NDF content, and the proportion of sample dry matter (DM) collected in a ≥1.18-mm sieve is commonly used as the physical effectiveness factor in the equation. The peNDF1.18 contents of the high, medium and low diets were 25.97%, 21.10% and 17.94% (P < 0.05). In addition, the proportion of particles collected on the 19-mm, 1.18-mm, and pan sieves changed linearly with an increase of TMR mixing time. Mean particle-size distributions of diets were 11.43, 24.11, 30.70 and 33.68 for 19 mm, 8 mm, 1.18 mm and pan, respectively. Eating rate and ruminating and chewing efficiencies were significantly decreased with reduced peNDF content, and DM intake was increased significantly (P < 0.05). Lower peNDF content reduced the total number of chews significantly (P < 0.05). Total time spent chewing associated with eating was not affected by peNDF contents. Digestibility of DM, crude protein and crude fat decreased with reducing peNDF content in the diet, but there was no significant difference among the three groups. These results indicated that peNDF affects intake, digestibility and chewing activity in beef cattle. Therefore, high levels of peNDF appears to improve TMR, as it can increase efficiency and may prevent ruminal disorders in Hanwoo steer.