EFFECTS OF OVEN-DRYING TUBERS OF 2 HIGH-PROTEIN SWEET-POTATO VARIETIES AT DIFFERENT TEMPERATURES ON THEIR FEEDING VALUE IN BROILERS

1. Unpeeled tubers from 2 high-protein varieties of sweet potato (whit e-fleshed Bosbok, and orange-fleshed Carmel) were chipped and oven-dri ed at 40, 60, or 80 degrees C, to examine the effects on nutritive val ue. The dried ground chips were substituted for maize at 500 g/kg and the diets fed to day-old, Ross-l broiler chicks for 3 weeks. 2. Compar ed with Carmel, Bosbok had a lower crude protein content (90 v. 138 g/ kg DM) and trypsin inhibitor activity (TIA) (3 v. 5 mg of trypsin inhi bited per g flour). Processing did not significantly affect TIA, but t he lysine and cystine contents were lowered and the starch content rai sed as the drying temperature increased. However, whereas this was ref lected in increased reducing sugars in Carmel, there was no trend in B osbok. 3. The results of in vitro pancreatin digestibility and total d ietary fibre assays showed variety and processing temperature to be si gnificant factors influencing the nutritive value of sweet potato tube rs, with a variety X temperature interaction also being indicated. The interaction was also observed for weight gain, dry matter intake, wat er:food intake ratios, excreta water content, presence of bile in excr eta and liver weights. The best growth was obtained with Bosbok dried at 60 degrees C, for which liveweights at 21 d were 11% lower than for the maize controls.