Effect of either once or twice daily concentrate supplementation of wheat straw on voluntary intake and digestion in sheep

Abstract

Eighteen mature Merino ewes were used to study the effect of either once or twice daily concentrate supplementation of wheat straw on voluntary intake and diet digestibility. Diets consisted of wheat straw, fed as the only feed (S0) or supplemented with 0.450 kg of concentrate per day (850 g cracked barley grain, 120 g soya-bean meal and 30 g vitamin–mineral supplement per kg of concentrate) given either in a meal (S1) or in two equal meals (S2). Concentrate supplementation tended ( P<0.10) to reduce the daily intake of wheat straw (mean values 13.8, 10.4 and 11.3 g dry matter (DM) per kg live weight for S0, S1 and S2 diets, respectively), but total dry matter (DM) intake and apparent DM digestibility were increased ( P<0.01). Apparent digestibility of the diet and digestible organic matter (OM) intake were unaffected ( P>0.05) by the frequency of concentrate feeding. Rumen fermentation were studied using three rumen-cannulated Merino sheep in a 3×3 Latin square design. Concentrate supplementation decreased ( P<0.01) ruminal pH (mean values of 6.79, 6.03 and 5.98 for S0, S1 and S2, respectively) and increased ( P<0.05) ammonia–N concentration (40.0, 132.1 and 168.3 mg/l for S0, S1 and S2, respectively). Total volatile fatty acids (VFA) concentrations and molar proportions of butyrate, isovalerate and valerate were increased by concentrate feeding ( P<0.001, 0.05, 0.001 and 0.05, respectively), whereas the proportions of acetate and isobutyrate were decreased ( P<0.05). Increasing the concentrate feeding frequency to twice daily did not affect ( P>0.05) ruminal pH, ammonia–N or VFA concentrations, but increased ( P<0.01) the molar proportion of isovalerate (0.832 and 1.135% for S1 and S2, respectively). Concentrate supplementation decreased ( P<0.05) the in situ degradation rate of both wheat straw neutral-detergent fibre and concentrate crude protein (CP), but the pattern of concentrate feeding did not affect ( P>0.05) the in situ degradation of either wheat straw or concentrate.