Effect of heat treatment on forage quality of bio-fortified orange fleshed Ipomea batatas crop residues and roots

Abstract

Post-harvest management of sweet potatoes (SP) crop residues preserves nutrients, deactivates inhibitor compounds and improves rumen degradation. The aim of the study was to determine effects of drying crop residues and heating roots on forage value of a bio-fortified orange fleshed sweet potato (OFSP) variety in South Africa. The crop was harvested at maturity and roots separated from crop residues. Roots were washed, sliced and divided into three portions as SP roots that were frozen at-4°C for 4 weeks, SP 70-oven dried at 70ºC for 8 days and SP 80-80ºC for 7 days. Aboveground crop residue were separated into portions of vines and leaves (SPVL f) and leaves and petioles only (SPL f). A subsample of each portion was air dried for 7 days (SPVL d and SPL d , respectively). Chemical composition and in sacco organic matter disappearance were determined. Crude protein (CP) was higher (P<0.05) in SPL d (24.9% CP DM) compared to fresh material with 6.5%. Neutral detergent fibre (NDF) and insoluble CP (NDFICP) were higher after drying, non-fibre carbohydrates (NFC) declined and vitamin A declined. Effective degradability (ED) was higher than for Lucerne hay and differed between SPVL d and SPL d 77.6% and 81.3% at kp=0.05; respectively. The SP roots were low in CP, ether extracts and fibre; had higher NFC (77% DM) and gross energy (4.1 Mcal/kg DM) compared to SP 70 and SP 80. The SP 80 roots had the least NFC (P<0.01) and highest amount of fibre. Calcium, phosphorus and vitamin A were negligible post heating. Rate of degradation (c h-1) and ED was highest with SP 80 (0.22 and 91.3%; kp=0.03) and lowest with SP roots (0.135 and 81.7%). Drying OFSP crop residues and heating roots affected nutrient profiles however, forage degradability improved.