Nutrient Utilization in Local Mixed Genotype Growing Pigs Fed Wheat-Based Protein Concentrates Blended with Sweet Potato Roots Ensiled with or without Vines

Abstract

Background: Feeding sweet potato (Ipomoea batatas, L. (Lam)) roots and forage to pigs is characteristic of smallholder farming in tropical countries and particularly the use of indigenous breeds and their crossbred progeny (mixed genotype, MG) growing pigs.Presenting forage as ensiled, fermented feed, is a recent technology to smallholder pig feeding in the Pacific region, which until now was not tested for metabolic contribution to effective nutrition for MG pigs and towards reducing the feed costs of production.Objectives: To determine the nutritional utilization of sweet potato for mixed genotype local pig breeds.Methods: Two metabolic trials tested the total tract apparent digestibility (TTAD) of nutrients and N balance in MG growing pigs fed ensiled SP roots (ER) or roots and vines (ERV), blended with two protein concentrates at 380, 400, 430 and 500 g/kg DM into four treatment diets, ER380, ER430, ERV400 and ERV500, compared against a standard wheat-based commercial pellet diet (STD). The trials were conducted using a 4 × 4 Latin Square design with two sets of four MG pigs at 23 kg (Trial 1) and 27 kg (Trial 2) starting BW. The trial pigs were offered one of four diets interchanged during four 8 d periods, with a 5 d adaptation phase and 3 d for total collection of faeces and urine. Pigs were housed in all-steel metabolic cages (1.0 m × 1.0 m × 1.5 m) on stands 0.7 m above floor level.Results: DMI was higher (2,290-2,739 g/d) for pigs on the SP-based diets (p < 0.05), ADG in Trial 1 was lower (686-718 g/d) but in Trial 2 was similar (944-1072 g/d) to pigs fed STD (p > 0.05), while the FCR (2.72-3.70) was higher than STD (p < 0.05) in both trials. DM, OM, CF, fats (EE), carbohydrates (NFE) and energy coefficients of TTAD were superior on the SP-based diets, but Ash, Ca and Total P CTTAD were reduced compared to STD (p < 0.05). N retained (g N/d) differed between the diets; 27.1 (ERV400), 20.8-24.8 (ER430), 27.7-29.0 (ERV500), 30.8-31.2 (STD); and did not reflect dietary CP or amino acid levels, dietary fibre content, or energy digestibility.However, N retention (NR% intake) and utilization (NR% digested) was inferior to STD for all SP-based diets except ER380 (Trial 2). Higher faecal N (g/d) (P < 0.05) suggested increased hind gut fermentation in pigs fed on SP-based diets, whereas higher urine N (g/d) (p < 0.05) indicated a lower N requirement. Conclusion:Dietary fibre in SP vines reduced nutrient utilization for growth but MG pigs adapted over time. Reduced protein and amino acid supplementation were recommended for MG pigs.