Effect of regrowth age on intake and digestion of Digitaria decumbens consumed by Black-belly sheep

The intake and digestion of fresh Digitaria decumbens grass were studied fo llowing the stage of regrowth. Six rams (mean liveweight: 40.8 +/- 0.6 kg) received successively a 14, 28, 42 and 56-day old forage during four 4-week periods. The range of variation of crude protein and acid detergent fibre content (g/kg) of the forages was 57-130 and 380-442, respectively. The DM intake (g/kg W-0.75) and the organic matter total tract digestibility decre ased from 83 to 56 and from 0.728 to 0.628, respectively, between 14 and 56 days of regrowth. The fractional degradation rate (h(-1)) of dry matter in the rumen, estimated by the nylon bag method, decreased curvilinearly with a mean daily rate of 0.0010. A curvilinear relationship was recorded betwe en the rumen turnover rate and forage regrowth stage. The mean daily decrea se (per hour per day) was 0.0005. The total nitrogen duodenal flow (g per d ay) decreased from 22.7 to 11.6 between 14 and 56 days. The mean efficiency of microbial protein synthesis was similar with the four diets (31.8, S.E. 2.2 g microbial nitrogen/kg organic matter apparently digested in the rume n). In conclusion, intake, digestibility and duodenal nitrogen flow are hig h with the 14-day D. decumbens. As a consequence, the nutritive value of th e latter is similar to the one of a good temperate grass forage. Good nutri tive value of a 14-day old D. decumbens and fast maturation and lignificati on in C-4 forage before the first month of regrowth suggest the need to inv estigate ruminant feeding strategies with forages younger (<28 days) than t hose classically used when the aim is the increase in animal individual per formances in humid tropical area. (C) 2000 Elsevier Science B.V. All rights reserved.