Weight gain increased from −8 to 43 g/day with increasing level of legume supplementation at 22 and 30 g DM/kg W0.75 at which point Madras thorn was 43% of the diet. The results are similar to Norton (1994a) who observed a linear increase in weight gain for goats fed on barley straw and supplemented with increasing levels of Sesbania sesban up to 33% DM, supplementation while at 65% DM supplementation there was a reduction in weight gain. Norton (1994a) also noted that maximum gains are achieved when supplements are provided at 40–60% of the total DM intake. The 43 g/day gain compares with the local Cambodia goats supplemented with 1 kg Gliricidia foliage/day grazing on natural pastures ( Him Aun, 2002). Sawe et al. (1998) reported higher weight gains on goats feeding leaves of indigenous trees.
Positive N balance was recorded for all goats, with maximum N retained being recorded with goats fed 22.5 g DM/kg W0.75 or more of Madras thorn. The N retained between 22.5 and 30 g DM/kg W0.75 treatments was similar, however higher N loss was recorded with the 30 g DM/kg W0.75 treatment. The treatment where N was most efficiently utilized was 22.5 g DM/kg W0.75 (Table 3). Similar results were shown by Nyanganga (2001) supplementing wether fed straw increasing levels of Acacia brevispica where N balance dropped beyond 20% DMI of legume inclusion. The increase in weight gain on Madras thorn supplementation could be explained by increase in digestibility and nutrient intake especially N. Similarity in weight gain at 22.5 and 30 g DM/kg W0.75 supplementation could be as a result of high CP intakes with low energy content thus limiting factor to proper utilization of feed N. The energy content at 30 g DM/kg W0.75 was below the level recommended by Peacock (1996) for higher growth rate. Ondiek et al. (1999) recorded the highest live weight gain from supplementing with the gliricidia–maize bran mixture than gliricidia alone. Better performance in gliricidia-bran supplemented group may be explained by the phenomenon of synchronization of energy and protein. Synchronization of ME and N in the gliricidia-bran mixture could have resulted in a better supply of energy and protein to microbes and hence a more efficient microbial protein synthesis ( Sinclair et al., 1995; cited by Ondiek et al., 1999).