Abstract 299

Eys,-JE-van; Mathius,-IW; Pongsapan,-P; Johnson,-WL

Dep. Animal Science, Box 7621, Raleigh, NC 27695-7621, USA.

Journal-of-Agricultural-Science,-UK. 1986, 107: 2, 227-233; 19 ref.

Foliage from tropical legume trees was used to supplement Napier grass (NG) diets for growing goats. The grass contained 12% protein on average. NG and foliage of Gliricidia maculata, Leucaena leucocephala and Sesbania grandiflora were subjected to in situ microbial fermentation and subsequent treatment with acid-pepsin solution. Nitrogen rendered soluble after incubation for 2 h was 46 and 43% for NG and sesbania respectively, compared with 27% for gliricidia and leucaena. Average rate of protein disappearance between 2 and 24 h incubation in the rumen was 2.6%/h for the legumes and 1.0%/h for NG. The proportion of water-insoluble, rumen-degradable protein from the legumes was larger than that from NG. Intake of NG by goats supplemented with gliricidia or leucaena at 15% of the DM intake from NG was lower than that of controls receiving no legume supplememt. NG intake did not differ between controls and sesbania-supplemented goats. There was no difference among diets in total DM intake, intake of cell wall constituents or digestibility. Average daily gain for control goats was -1 g/day, compared with 21 g/day for supplemented goats. Feeding with formaldehyde-treated soyabean meal (F-SBM) as a supplement to either NG or NG-legume diets increased intake of DM and weight gain of goats. NG intake of goats supplemented with only F-SBM was higher than that of control animals. The efficiency of N utilization from F-SBM was higher than that in the legumes, but replacement of legumes by F-SBM above 4% in the diet had no effect on weight gain or efficiency of utilization. It was concluded that NG of 6-8 weeks' regrowth with 12% crude protein did not provide sufficient protein for growing goats owing to inefficient protein utilization. The increase in efficiency of protein utilization on supplemented diets is mainly associated with the larger proportion of water-insoluble, rumen-degradable protein and possibly acid-pepsin soluble protein in tropical tree legumes.