An investigation of feeding level effects on digestibility in cattle for diets based on grass silage and high fibre concentrates at two forage:concentrate ratios

Abstract

This experiment investigated the effect of feeding level on diet digestibility at two forage:concentrate ratios for diets containing grass silage. Four rumen fistulated Holstein–Friesian steers were used in a latin square experiment comprising a 2×2 factorial arrangement of treatments. Treatments were maintenance and 1.6×maintenance feeding level and 500 or 850 g of soya hulls/kg DM. Digestibility was determined by total collection, with fractional soya hulls (k1p) and fractional solute outflow rate (k1f) determined for the rumen using Cr-mordanted soya hulls and Co-EDTA, respectively. Rate of digestion was determined in-sacco. Increasing feeding level and soya hulls inclusion decreased diet DM, OM, CP, NDF, ADF and GE digestibility ( P<0.01). The depression due to feeding level was greater for 850 g/kg DM soya hulls diets for GE ( P<0.05), DM ( P=0.06) and OM ( P=0.06) digestibility. Rate of slowly degradable soya hulls DM and NDF digestion was lower ( P<0.05 and P=0.07) for 850 g/kg DM soya hulls diets. Soya hulls k1p and k1f increased with feeding level but only the increase in k1f was significant ( P<0.01). Diet OM, NDF and GE digestibility were positively related to rumen pH 6 h after feeding ( P<0.01; R 2=0.50 to 0.69). These results suggest that lower rumen pH values may be an important component of the larger digestibility depressions often observed for high concentrate diets.