Bioconversion of Sweet Potato Leaves to Animal Feed

Background: High cost of conventional animal feed ingredients in Nigeria has made it necessary to search for alternative local sources of feed. Crop residues including sweet potato leaves abound in Nigeria. These have been explored as feed sources. The ability of microorganisms to convert agricultural wastes to more useful products could be harnessed to produce feed from sweet potato leaves which can be obtained in high abundance at low cost.

Aim: To examine the possibility of converting sweet potato leaves to animal feed through fermentation with a co-culture of Chaetomium globosum and Saccharomyces cerevisiae.

Materials and Methods: Triplicate samples of sweet potato leaves were fermented with a co-culture of C. globosum and S. cerevisiae for 21 days at 25±2°C and the effects of fermentation on nutrient composition was determined. Fermentation and control samples were analysed for proximate, amino acids, and elemental contents. Acute oral toxicity of the fermented leaves was determined by the fixed dose method using mice and rats. Feed value of the fermented sweet potato leaves for mice was determined. Parameters assessed included feed intake, protein intake, weight gains, feed efficiency ratio, and protein efficiency ratio.

Results: Crude protein, crude fat and ash contents increased by 97.5%, 265.3% and 12.3%, respectively, while crude fibre and nitrogen free extract values decreased by 22.7% and 61.4% respectively. Energy content increased by 14.5%. The observed changes in the values of these nutritional components were significant (P < .05). The percentage dry matter values of all the amino acids analyzed (lysine, histidine, arginine, aspartic acid, threonine, glutamic acid, proline, glycine, alanine, cystine, valine, methionine, isoleucine, leucine tyrosine and phenylalanine) were found to increase, with the contents of seven of the amino acids increasing significantly. Calcium, phosphorus, potassium and magnesium contents increased significantly while those of copper and iron decreased. The fermented leaves were found to be non toxic to mice and rats. Sole use of fermented sweet potato leaves by the mice led to depression in feed intake, weight gain, feed efficiency ratio and protein efficiency ratio. Mice fed with commercial mice feed supplemented  with 5% fermented sweet potato leaves had higher weight gains, feed efficiency and protein efficiency ratios than those fed on the commercial mice feed.

Conclusion: Fermentation of sweet potato leaves with a co-culture of C. globosum and S. cerevisiae improved the nutritional value of the leaves. Fermented sweet potato leaves can be included in mice feed up to 5% without negative effects. Sole use of fermented sweet potato leaves as feed for mice and possibly other animals would require mineral supplementation, energy enhancement, and further crude fibre reduction.

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