Nutrient utilization in grower pigs fed boiled, ensiled or milled sweet potato roots blended with a wheat-based protein concentrate

Sweet potato (SP) roots are highly palatable and digestible for pigs as fresh, boiled, ensiled or dried feed. The form of presentation and blending with other highly digestible protein ingredients could improve nutrient utilization by grower pigs. A metabolic experiment was conducted utilising a 4 × 4 Latin Square design with four (Landrace × Large White) × Duroc pigs at nine weeks of age (26.5 ± 1.4 kg), where four dietary treatments offered ad libitum over four consecutive eight-day feeding periods tested the hypothesis that there would be no difference in nutrient digestibility and utilization in pigs fed SP roots when prepared as boiled (BR), ensiled (ER) or milled roots (MR) and blended with a complementary protein concentrate, and compared against a standard wheat-based pig feed (STD). SP products were blended with protein concentrate at 43%:57% DM, and provided total lysine:DE ratios of 0.57, 0.58, 0.60 and 0.58 g/MJ DE for BR43, ER43, MR43 and STD respectively. DM intake, ADG and FCR were similar (p > 0.05) among treatments. Coefficient of apparent total tract digestibility (CATTD) of DM, OM, fibre, calcium, total phosphorus and energy retention (%) in SP root diets were superior to STD (p < 0.05). Ash CATTD of ER43 and MR43 were improved over STD whereas BR43 was similar to all three diets. CATTD of fats (EE) was similar. Protein (CP) CATTD of BR43 was superior to MR43 and STD whereas ER43 was similar to the other three diets. N intake (g/d), N digestibility (% intake) and N utilization (% digested) were similar. N retained on STD (30.6 g N/d) and MR43 (30.4 g N/d) were similar. The much higher N retained on BR43 (35.4 g N/d) and ER43 (35.8 g N/d) was due to a significant shift in N loss from urine (8.2 and 7.0 g N/d) to faeces (13.7 and 10.1 g N/d) which, combined with greater OM digestibility and energy retention, suggested increased microbial use of N in the hindgut. The SP diets were highly digestible and provided improved nutrient utilization, ADG and FCR in pigs compared to the wheat-based commercial feed.