Effects of oven-drying tubers of two 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 (white-fleshed Bosbok, and orange-fleshed Carmel) were chipped and oven-dried at 40, 60, or 80 degrees C, to examine the effects on nutritive value. The dried ground chips were substituted for maize at 500 g/kg and the diets fed to day-old, Ross-1 broiler chicks for 3 weeks. 2. Compared 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 inhibited per g flour). Processing did not significantly affect TIA, but the lysine and cystine contents were lowered and the starch content raised as the drying temperature increased. However, whereas this was reflected in increased reducing sugars in Carmel, there was no trend in Bosbok. 3. The results of in vitro pancreatin digestibility and total dietary fibre assays showed variety and processing temperature to be significant factors influencing the nutritive value of sweet potato tubers, with a variety temperature interaction also being indicated. The interaction was also observed for weight gain, dry matter intake, water: food intake ratios, excreta water content, presence of bile in excreta 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.