THE UTILIZATION OF (ERAGROTIS TEF) STRAW BY SHEEP FED SUPPLEMENTARY FORAGE LEGUMES WITH OR WITHOUT EITHER CRUSHED MAIZE GRAIN OR WHEAT BRAN

This study examined the interaction of high energy substrates (ES; cru shed maize grain (MG) and wheat bran (WB)) with forage legumes (FLs), such as Lablab purpureus hay, sun dried leaves of Sesbania sesban and tagasaste (Chamaecytisus palmensis), on ruminal microbial activity (in dexed by the degradability and digestibility of teff (Eragrotis tef) s traw (TS), urinary excretion of purine derivatives (PD)) and on nitrog en retention. The diets comprised TS fed alone ad libitum (TSA) or TSA supplemented with either of the above FLs (175 g/day) with or without 47 g/day of either MG or WE. The 10 diets were fed to 20 ruminally ca nnulated sheep in two periods during which each of the degradabilities of TS and of the FL corresponding to that which the sheep were consum ing were determined in sacco. The particulate rate of passage was also determined using chromium mordanted TS. Forty castrated male Ethiopia n Menz sheep were used in a randomised complete block design to determ ine the effects of the above diets on intake, digestibility, urinary P D, microbial N synthesis and N retention. Both the potential and the e ffective degradabilities indicated that sesbania was the most degradab le, and lablab the least. Supplementation with FLs alone increased the rate of degradation of TS by 50 to 142%, the rate of passage of parti cles (k(p)), the intake of TS, dry matter (DM), organic matter (OM), n itrogen (N) and neutral detergent fibre (NDF); had no effect on the di gestibility of DM, OM, teff and NDF; increased faecal N, urinary N, N retention, urinary allantoin, total and microbial PD, microbial N and the efficiency of microbial N synthesis. Forages were similar in the d egradation rate of TS but differed in the intake of TS, DM and OM in t he order: sesbania > tagasaste > lablab. Lablab diets sustained higher k(p) than either the sesbania or tagasaste diets. Sesbania diets, com pared to lablab or tagasaste diets, depressed the digestibilities of D M, OM, NDF, ADF and TS; increased faecal, urinary and retained N, urin ary allantoin, total and microbial PD, microbial N and efficiency of m icrobial N synthesis. Further supplementation with high ES depressed k (p), tended to depress (P > 0.05) the degradation rate of TS by 14-45% , and that of FLs by 21-47%; increased faecal N, retained N, urinary a llantoin, total and microbial PD, microbial N and the efficiency of mi crobial N synthesis; had no effect on digestibility and urinary N. Mai ze depressed the digestibility of ADF and urinary N, but increased uri nae allantoin relative to wheat bran while both energy substrates elic ited similar N retention and microbial N synthesis. Supplementing stra w diets with FLs is beneficial in terms of intake, microbial N synthes is and yield. These benefits correlate positively with the degradabili ty of FLs and are further improved by a complementary high energy subs trate. (C) 1998 Elsevier Science B.V. All rights reserved.