Ipomoea batatas

Sweet potato

Pedro L. Domínguez, Titular Researcher in Pig Nutrition, Nutrition Departament, Swine Research Institute, Gaveta Postal No. 1, Punta Brava, Ciudad de La Habana, Cuba.

Useful references: 612

Sweet potato is a creeping plant with perennial vines and adventitious roots, some of which produce swollen tubers. It is an ancient food plant from tropical America and the Pacific islands, and several varieties of sweet potato are now extensively cultivated in many parts of the world. The mejor producing countries are Japan, Indonesia, Brazil, Korea, China, India and Uganda, with their production ranging between one and four million tons per year. Substantial quantities are also produced by the Philippines, the USA, Malaysia and several other countries.

It can be grown in well drained loamy soil which is rich in humus to provide a warm and moist environment to the root, requiring at least four month of warm weather; it doesn't stand.

Chemical composition

Low protein, fat and fibre were found in the roots, but the high nitrogen-free extract fraction in this tuber is indicative of its potential value, mainly as an energy source. The vines have a lower carbohydrate content but higher in fibre and protein and their principal nutritive value is as a source of vitamins and protein.

Carbohydrates generally make up between 80 to 90 % of the dry weight of sweet potato roots but the uncooked starch of the sweet potato is very resistant to the hydrolisis by - amylase. When cooked, their susceptibility to the enzyme increases. Thus, after cooking, the easily hydrolysable starch fraction of sweet potato increases from 4 % to 55 %. The content of trypsin inhibitors of the raw sweet potato roots could decrease the protein digestibility in mixed feed. The vines will not produce this effect because they do not contain them in great quantities. This trypsin inhibitor could be destroyed or lowered by preheating raw sweet potato roots.

Roots

Cooking sweet potato increased pig live-weight gain when compared with raw sweet potato and Pigs grazing sweet potatoes require

500 g protein concentrate per pig per day for optimal growth. Several results have confirmed that the performance of pigs fed diets containing dried sweet potato chips was not comparable to that of pigs fed corn but daily gain and feed/gain ratio were acceptable when the pigs were fed diets where sweet potato chip substituted half of the corn or at levels near 40 % in the diet. However, cooked and mashed sweet potatoes may totally replace maize for fattening pigs provided an adequate protein supplementation is used. Sweet potato root meal can be included up to 50 % in poultry feeds with good results if properly supplemented with protein. The fresh tubers are palatable for cattle and sweet potato meal was found to be 90 % efficient as a feed for lactating cows when compared to corn meal feed.

Foliage

The vines serve as a nutritive and relished green feed for cattle. The feeding value of vines is close to that of alfalfa.

Fresh sweet potato vines are palatable to cattle and a cow of

400-500 kg can consume 50-70 kg daily. An increased proportion of fresh sweet potato vines produced more milk. The supplementation of sweet potato-forage improves feed intake and weight gain of young bulls fed sugar cane stalks.

Sweet potato vine meal can be used in poultry rations both as a source of protein or xantophyll pigment. The xantophyll of sweet potato vines is a good pigmentation agent for egg yolks and broiler skins.

Sweet potato fresh foliage has been used for weaned piglets substituting 10 % of the cereal concentrate with satisfactory animal performance both from the point of view of weight gain and feed conversion and also related to mortality and herd culling.

The supplementation of standard diets with sweet potato foliage did not improve the performance of pigs. The use of fresh foliage, substituting 25 and 50 % of soybean meal as a protein source in sweet potato roots-soybean diets, decreased the intake of dry matter probably due to the bulkiness of this feed. Nevertheless, with the low level of substitution of soybean, meal, feed conversion was similar to that obtained using sweet potato-soybean diets.