Comparison of fresh and dried Digitaria decumbens grass intake and digestion by Black-belly rams

Abstract

The intake and digestion of fresh and dried Digitaria decumbens grass by rams was compared using a 2×2 factorial design. The experiment took place in Guadeloupe (French West Indies) in 1996. Eight rams (mean liveweight: 45·7±3·1 kg) were maintained in metabolism cages. Digitaria decumbens grass was cut daily and distributed to four of them, the other four were fed the following day with the equivalent forage which had meanwhile been dried for 20 h at 60°C. Chemical composition (g/kg of dry matter (DM)) of the two diets based on neutral detergent fibre (NDF, 713, S.E. 18), acid detergent fibre (ADF, 361, S.E. 13) and crude protein (CP, 90, S.E. 4) was similar. The DM intake (61·0 and 53·2 g/W^0·75, S.E. 2·0, P<0·05), the NDF (0·753 and 0·727, S.E. 0·004, P<0·011) and CP (0·588 and 0·544, S.E. 0·014, P<0·09) total tract digestibility of fresh and dried herbage were different. Nylon bag estimates of effective DM degradability and fractional degradation rates (per h) in the rumen were 0·436, 0·414 (S.E. 0·005, P<0·004) and 0·048, 0·038 (S.E. 0·002, P<0·02) for fresh and dried grass, respectively. Rumen digestibility of organic matter and NDF were 0·516, 0·541 (S.E. 0·021) and 0·763, 0·692 (S.E. 0·019), respectively. The rumen turnover rates of particles (per h) were 0·024 and 0·015 (S.E. 0·001, P<0·05) for fresh and dried forage respectively. The efficiency of microbial protein synthesis (g microbial nitrogen/kg organic matter apparently degraded in the rumen) was similar with the two diets : 33·5 and 33·0 (S.E. 3·3, P<0·9) for fresh and dried forage respectively. In conclusion, fresh Digitaria decumbens was nutritionally superior to dried. This is probably due to a faster degradation rate and a lower rumen retention time of the fresh forage.