Twenty five rumen fistulated Ethiopian Menz sheep were used in a compl
etely randomized block design to determine roughage utilization when d
ifferent types of supplements (sesbania, leucaena, cotton seed cake (C
SC)) and forms (fresh or dry leucaena) were fed. The chemical composit
ion, intake, digestibility, nitrogen balance and rumen degradability c
oefficients were determined. Rumen pH and ammonia-nitrogen (NH3-N) lev
els were estimated in samples taken at 1, 2, 3, and 6 h after feeding.
There was substitution of teff straw dry matter by the supplements. F
resh leucaena effected the highest substitution. Supplementation enhan
ced (p < 0.05) the dry matter degradation (DD) of teff straw at 6 and
12 hours of incubation but not (p > 0.05) for the other incubation tim
es. There were no significant differences (p > 0.05) between treatment
s in the degradation constants: readily soluble component (a) slowly d
egradable fraction, (b) potential degradability (PD = a + b) and rate
of degradation (C) and for rumen NH3-N concentration, the ranking was
CSC > sesbania > dry leucaena > fresh leucaena > teff straw alone (p <
0.05). The particularly high substitution rate observed with fresh le
ucaena might suggest that bulkiness may be a limiting factor in the in
take of low quality roughages supplemented with tree leaves. The lower
DM and OM digestibilities of the supplemented diets were attributed t
o substrate preference by rumen cellulolytic bacteria. Excessively hig
h levels of rumen NH3-N (328 mg/l) in the CSC diet resulted in high ur
inary nitrogen losses (r(2) = 0.32; p < 0.001) leading to low N balanc
e, This may suggest that for the utilization of poor quality tropical
roughages, moderate levels of rumen NH3-N sustained over a longer peri
od may be needed.