African Journal of
Agricultural Research

  • Abbreviation: Afr. J. Agric. Res.
  • Language: English
  • ISSN: 1991-637X
  • DOI: 10.5897/AJAR
  • Start Year: 2006
  • Published Articles: 6578

Full Length Research Paper

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

Florence Veronica Nherera-Chokuda
  • Florence Veronica Nherera-Chokuda
  • Agriculture Research Council, Private Bag x02, Irene, Pretoria, South Africa.
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Christiaan Jacobus Smit
  • Christiaan Jacobus Smit
  • University of South Africa, Johannesburg, South Africa.
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Mukengela Claude Muya
  • Mukengela Claude Muya
  • Agriculture Research Council, Private Bag x02, Irene, Pretoria, South Africa.
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Joyce Ledile Marumo
  • Joyce Ledile Marumo
  • North-West University, Private Bag x2046, Mmabatho, 2735, South Africa.
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  •  Received: 26 January 2017
  •  Accepted: 04 April 2017
  •  Published: 03 August 2017


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 SProots that were frozen at -4°C for 4 weeks, SP70- oven dried at 70ºC for 8 days and SP80 -80ºC for 7 days. Aboveground crop residue were separated into portions of vines and leaves (SPVLf) and leaves and petioles only (SPLf). A subsample of each portion was air dried for 7 days (SPVLd and SPLd, respectively). Chemical composition and in sacco organic matter disappearance were determined. Crude protein (CP) was higher (P<0.05) in SPLd (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  SPVLd and SPLd 77.6% and 81.3% at kp=0.05; respectively. The SProots were low in CP, ether extracts and fibre; had higher NFC (77% DM) and gross energy (4.1 Mcal/kg DM) compared to SP70 and SP80. The SP80 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 SP80 (0.22 and 91.3%; kp=0.03) and lowest with SProots (0.135 and 81.7%). Drying OFSP crop residues and heating roots affected nutrient profiles however, forage degradability improved.

Key words: Sweet potato, vines and leaves, vitamin A, rumen degradation, non-structural carbohydrates.