Evaluation of tagasaste (Chamaecytisus palmensis) forage as a substitute for concentrate in diets of sheep

A feeding trial was carried out for 90 days to asses the supplementing effect of tagasaste forage as a substitute for a concentrate supplement (wheat bran-noug seed cake (Gizotia abyssinica) mixture in 3:1 proportion) using 24 Menz male sheep (initial weight of 18.3 +/- 1.6 kg). The sheep were fed on natural pasture hay as basal diet. The treatments were iso-nitrogenous supplements of 100% concentrate offered at 200 g DM/sheep/day (T1), 67% concentrate +33% tagasaste (T2), 33% concentrate +67% tagasaste (T3) and 100% tagasaste (T4). Digestibility tests of treatment diets were done for 10 days following the feeding trial using the same experimental animals. At the end of the experiment, carcass parameters were also evaluated. In situ degradability of feeds was determined using three rumen fistulated crossbred steers. Tagasaste forage contains more CP (215 g/kg), ADF (221 g/kg), ADL (69 g/kg); and less NDF (351 g/kg) compared to the concentrate. The concentrate had a high immediately soluble fraction (a), and a low insoluble but potential degradable matter (b), while tagasaste had a low a and higher b values and the overall potential degradability was 755, 702, and 586 g/kg, for tagasaste, concentrate and natural pasture hay respectively. Tagasaste forage had also shown higher rates of degradation (c) compared to the concentrate which might increase the total effective degradability. In the feeding trial the supplements made 26.8, 27.0, 28.3 and 29% of the total dry matter (DM) intake for T1, T2, T3, and T4, respectively. Increasing the inclusion of tagasaste forage significantly (P<0.01) decreased the daily total DM intake of the basal diet and total metabolizable energy (ME), and increased the CP intake. The average weight gain of sheep did not show significant difference (P>0.05), but had a decreasing trend, with 44.4, 41.4, 38.9 and 38.1 g/sheep for T1, T2, T3, and T4, respectively. The in vivo digestibility of DM and nutrients generally followed the order of T1 > T2 > T3 > T4. The dressing percentage of the carcass was 40.4% and all other parameters measured did not show significant variation due to treatment diets (P>0.05). However, weight of liver, kidney and spleen was higher for sheep fed with higher tagasaste forage diet. The result of this study revealed that tagasaste can substitute wheat bran-noug seed cake concentrate mixture as a protein supplement. Options to increase the low ME and minimize the effect of the anti nutritional factors will improve nutrient digestibility in tagasaste forage and will enhance the overall efficiency of feed utilization. (C) 2007 Elsevier B.V. All rights reserved.