Ffoulkes et al., 1978. Livest. Res. Rural Dev., 3 (3): 186-192

Sixteen bulls of 216 kg initial weight were used to compare forage from cassava (4% of liveweight) or sweet potato (5% of liveweight) with and without supplementation of 400 g/d of soybean meal in a 2 x2 factorial design with 2 replications using a basal diet of molasses containing 2.5% urea fed on a free choice basis. Rate of liveweight gain on sweet potato forage was increased significantly by the addition of soybean meal (from 570 to 784 g/d); on cassava forage there was a tendency for the same effect but the difference was not significant (from 853 to 944 g/d). The effects of the forages (and soybean supplement) appeared to be mediated through effects on voluntary intake which in turn was closely related to liveweight gain (r2=.75 for gain and DM intake, and r2= .69 for gain and protein intake). There was a significant interaction between the effects of the different forages and the level of soybean meal on the feed conversion ratio. In the absence of soybean meal, cassava forage was better than sweet potato; but in the presence of soybean meal (ie when protein was not limiting) the opposite effect was observed. The importance of the results of this experiment relate to the general development of cattle feeding systems based on the use of high levels of molasses/urea, in that they offer the perspective for achieving high levels of animal performance without the need to use conventional protein supplements which have become increasingly scarce and expensive during the last few years.