Sweet potato (Ipomoea batatas) forage
Description and recommendations
Sweet potato, patate douce, batata da terra, batata doce
Product names: sweet potato vines, sweet potato foliage, sweet potato leaves, sweet potato leaf meal, sweet potato vine meal
Convolvulus batatas L., Ipomoea apiculata M. Martens & Galeotti
Sweet potato (Ipomoea batatas (L.) Lam.) is a tuberous-rooted perennial mainly grown as an annual. The roots are adventitious, mostly located within the top 25 cm of the soil. Some of the roots produce elongated starchy tubers. Tuber flesh colours can be white, yellow, orange and purple while skin colour can be red, purple, brown or white. The stems are creeping slender vines, up to 4 m long. The leaves are green or purplish, cordate, palmately veined, borne on long petioles. Sweey potato flowers are white or pale violet, axillary, sympetalous, solitary or in cymes. The fruits are round, 1-4 seeded pods. The seeds are flattened (Ecocrop, 2010; Duke, 1983).
Sweet potato is cultivated for food in more than 100 countries. The area under cultivation was 8.5 million ha in 2009 and the worldwide tuber yield was 12648 kg/ha (FAO, 2010). The main sweet potato producers are China, Indonesia, Vietnam, India, Philippines and Japan in Asia, Brazil and the USA in the Americas and Nigeria, Uganda, Tanzania, Rwanda, Burundi, Madagascar, Angola and Mozambique in Africa (FAO, 2010).
Sweet potato tubers and leafy tops are mainly used as food (Duke, 1983). Sweet potato green parts are also a very valuable feed for livestock: vines and foliage can be dried and fed to cattle: they compare favourably with alfalfa hay (Duke, 1983). The tubers are relished by pigs and cattle and sweet potato tubers processing by-products can be fed to livestock (see the Sweet potato tubers datasheet).
Sweet potato vines and foliage can be fed to cattle, sheep, goats, pigs, rabbits and goats. Sweet potato forage can be an emergency supply of cattle feed in periods of water stress (drought or dry seasons) (Scott, 1992). It may be fed fresh, dried or ensiled, and makes make a very palatable silage with a pleasant fruity smell (Lebot, 2009). Sweet potato forage can also be dried, ground and mixed with sugarcane by-products.
For optimal leaf and stem production it is advisable to cut at intervals of 20 days with a defoliation of 50% of the total stems, since greater defoliation could reduce root production. Vines and leaves can be harvested three or four times per growing season (Lebot, 2009).
The center of origin of the sweet potato is thought to be located between the Yucatán Peninsula of Mexico and the mouth of the Orinoco River, in Venezuela. Sweet potatoes as old as 8000 years have been found in Peru. It has then spread to the Caribbean and Polynesia. It is now widely cultivated between 40°N and 32°S, up to 2000 m (and up to 2800 m in equatorial regions) (Ecocrop, 2010; Paneque Ramirez, 1992).
Sweet potatoes are cultivated wherever there is sufficient water to support their growth: optimal annual rainfalls for growth range between 750-2000 mm. When rainfall level is below 850 mm irrigation may be necessary but it should be stopped before harvest in order to prevent the tubers from rotting. Sweet potato is a warm-season annual, requiring 20-25°C average temperatures and full sunlight for optimal development. It needs a frost-free period of 110-170 days and growth may be hampered below 20°C average day temperatures. Sweet potato thrives in well-drained loamy soils with high humus content that provides warm and moist environment to the roots. Optimal soil pH is between 5 and 7 (Ecocrop, 2010; Ecoport, 2010; Paneque Ramirez, 1992).
Sweet potato is mildly drought-tolerant and can survive dry spells during the summer. However, low humidity impairs crop quality even if the plant resume growth after a water stress (Ecoport, 2010; Paneque Ramirez, 1992).
Huge amounts of sweet potato foliage are produced during tuber harvesting and the vines decay in 2 or 3 days. When animals cannot consume the forage in such a short time, it may be interesting to dry or ensile it using low-cost methods (Renaudeau, 2010, personal communication).
Sweet potato leaves and vines can be preserved by ensiling (Nguyen Thi Tinh et al., 2006; Lebot, 2009). After harvest, green and healthy material is chopped to 0.2-0.5 cm length and carefully prewilted during 1-4 h in the sun so that moisture content is reduced by 40-45%. The prewilted material is then thoroughly mixed with 10% rice bran, corn meal or cassava or sweet potato root meal and 0.5% salt. After mixture, the material is put in impermeable plastic bags, heavily pressed to remove the air from the mixture and the bags are carefully tight and dated (Nguyen Thi Tinh et al., 2006).
Sweet potato vines can be fermented with chicken manure: it results in higher crude protein, DM and ash contents than the other silages. Ensiling provides a good sanitary that does not contain aflatoxins, Salmonella, and Escherichia coli (Lebot, 2009).
Sweet potato is remarkably adapted to scarce conditions since it thrives even with very low inputs and minimal horticultural practices. It grows very quickly, has some tolerance of drought and provides high amounts of nutrients during the scarcer periods (Scott, 1992).
The vines contain trypsin inhibitors but at relatively harmless levels.
Sweet potato forage is mainly a source of protein and contains about 15-30% DM of crude protein but the forage quality depends on the proportion of leaves and stems, the latter containing much less protein than the leaves. Lysine is the main limiting amino acid (Le Van An, 2004). Unlike legume forages, it does not contain notable quantities of antinutritional factors.
Tables of chemical composition and nutritional value
The vines are separated from the roots after harvest and provide a nutritive and relished green feed for ruminants (Nguyen Thi Tinh et al., 2006). It is a suitable protein supplement for animals receiving low quality forage.
Digestibility and degradability
Dry matter digestibility was found to be 70% (Ffoulkes et al., 1978a) and dry matter degradability was in the 40-50% range (Etela et al., 2008a). Protein degradability of fresh sweet potato forage was found to be quite high (about 70%), but the undegradable dietary protein was lower than that of protein supplements of similar degradability (cottonseed meal and Gliricidia sepium) so that less digestible true protein is available to the animal for metabolism after digestion and absorption (Kabi et al., 2005).
A cow of 400-500 kg can consume 50-70 kg daily (Göhl, 1982). Sweet potato forage can be fed to dairy cows as a supplement to forages such as Guinea grass (Megathyrsus maximus) or sorghum silage (Etela et al., 2009; Etela et al., 2008b; Ashiono et al., 2006). Such supplementation results in lower DM intake, but higher ME utilization for milk production (Etela et al., 2009; Etela et al., 2008b). While it has no negative effect on milk quality, it can only sustain low levels of milk production and does not compare favourably with dried brewers' grains or cassava forage as a supplement for milk production, though it could help saving production costs for smallholders (Etela et al., 2009; Etela et al., 2008b; Lopez et al., 1998).
Growing and fattening cattle
Heifers fed on Napier grass (Pennisetum purpureum) and supplemented with sweet potato forage have lower DM intake than heifers fed on grass alone. Growth performance (500 g daily weight gain) is similar on grass and grass + sweet potato and lower than on grass+alfalfa (Kariuki et al., 1998)
In Zebu bulls, supplementation with sweet potato forage of a diet based on sugarcane stalks increased voluntary intake and live weight gain, which was explained by the protein in the sweet potato forage acting as a by-pass nutrient and by the physical nature of this forage improving the rumen function (Ffoulkes et al., 1978a). Addition of N urea in association with sweet potato forage supplementation resulted in further live weight gains. This was was possibly due to the improvement in the rumen ecosystem which may encourage microbial growth and create a demand for fermentable N (Meyreles et al., 1979).
Sweet potato vines were found to be a high quality feed for calves due to their high yield, palatability and crude protein content. When offered ad libitum to calves fed Napier grass, they did not significantly affect the average daily gains of calves, and up to half of the milk can be saved when sweet potato vines are fed as a milk replacer (Orodho et al., 1996). Calves fed on Napier grass and sweet potato forage alone did better than those fed on Napier alone, but less that those fed on Napier grass supplemented with mixtures of sweet potato vines and other legume forages such as alfalfa, desmodium, Leucaena leucocephala and Sesbania sesban (Lanyasunya et al., 2006).
The carrying capacity of sweet potato plots pruned for sheep feeding was comprised between 100 and 165 heads/ha and an interval of 6 weeks may be adopted to optimize yield and quality of the forage (Olorunnisomo, 2007a). Mixing sweet potato forage and roots resulted in better nutrient utilization and lower cost per kg of live weight gain was reduced. A 50:50 sun-dried mix maximized economic returns from cultivating sweet potato for sheep feeding (Olorunnisomo, 2007b). Sheep seem to prefer cassava leaves to sweet potato leaves (Haryanto et al., 1982).
Lambs grazing sweet potato leaves recorded daily weight gains around 50-60 g (Rondon et al., 1989).
Though fairly relished by goats, sweet potato vines have low CP intake, poor N retention and poor CP and DM digestibility (Katongole et al., 2009a). It compared unfavourably with cassava leaf meal or Sesbania grandiflora as it resulted in lower DM intake and lower live weight gain (Vo Lam et al., 2004). However, better results in DM intake and animal performance have been yielded when goats could get accustomed to sweet potato vines (Kebede et al., 2011). Poor animal performances (less than 15 g daily weight gain) are also recorded when sweet potato vines are used to supplement a diet of Napier grass (Pennisetum purpureum), maize bran and Leuceana leucocephala leaves (Katongole et al., 2009a). Higher animal performances (44 to 82 g daily weight gain) are obtained when sweet potato vines supplement a cottonseed cake and maize bran mixture at 1:4 ratio (Katongole et al., 2009b) or a low quality grass (Ischaemum aristatum var. indicum) (Aregheore et al., 2004), respectively. Hence, sweet potato vines provide sufficient crude protein and metabolizable energy to sustain goat meat and milk production in tropical conditions, even during scarce periods where standard feeds are lacking (Katongole et al., 2009b; Katongole et al., 2008; Nambi et al., 2001). Feeding goats with sweet potato vines provides cheap nitrogen and increases feed efficiency (Aregheore et al., 2004). Sweet potato vines could profitably replace 50% concentrate feed (78.4% wheat bran, 20.6% noug seed cake) in male goats diet (Kebede et al., 2011).
Goats seem to prefer cassava leaves to sweet potato leaves (Haryanto et al., 1982).
Sweet potato vines are one of the most promising protein sources coming from tropical forages for pigs (Bui Huy Nhu Phuc, 2000). Thanks to its high crude protein content, high CP digestibility (above 65%) sweet potato foliage in fresh, dried or ensiled form can be used as a valuable protein and amino acids source in low fibre pigs diets in tropical areas (Le Van An et al., 2004; Rodriguez et al., 2003; Barrios et al., 2002).
In small-scale pig farms, sweet potato foliage could replace up to half the protein normally provided through conventional feedstuffs such as soybean meal or fishmeal (Preston, 2006). Sweet potato foliage can be fed to pigs without any negative effects on health (Renaudeau, personal communication). In Vietnam, sweet potato foliage is much appreciated by the poorest pig farmers because it can be fed year-round and its use results in lower production costs and higher net income (Ngo Huu Toan et al., 2007). In Cuba, sweet potato crop, including roots as energy source and vines as a protein source, can compete with maize in pig feed in Cuban pig production (Dominguez, 1992).
Fresh sweet potato vines
Growing and fattening pigs
Fresh sweet potato vines can be profitably included in growing and finishing pigs diets as they enhance basal diet palatability, overall DM intake, nutrient digestibility and animal performances (Chiv Phiny et al., 2010; Chhay Ty et al., 2007; Nedunzhiyan et al., 2000). They are generally offered ad libitum (Chiv Phiny et al., 2010; Chhay Ty et al., 2007). Fresh sweet potato foliage palatability is rather high and compares favourably with other tropical foliages such as mulberry leaves (Régnier et al., 2010 (unpublished); Chiv Phiny et al., 2010). The average daily fresh sweet potato foliage intake is about 3 kg/d (500 g DM/d) for a 50 kg pig, and 750 g/d for fresh chopped vines (Régnier et al., 2010 (unpublished); Nedunzhiyan et al., 2000).
Fresh sweet potato vines can be used as the sole protein supplement, combined with other foliage such as mulberry leaves or cassava leaves or associated to a protein-rich (20-23%) supplement (Chiv Phiny et al., 2010; Chhay Ty et al., 2007; Gonzalez et al., 2003). However, they appear to have a lower nutritive value than cassava leaves, stylo (Stylosanthes guianensis) and duckweed (Du Thanh Hang et al., 2009)
Sweet potato fresh foliage offered to weaned piglets can substitute 10 % of the cereal concentrate with satisfactory animal performance (weight gain, feed conversion, mortality and herd culling) (Göhl, 1982). However, because of its bulkiness, fresh sweet potato foliage cannot be included in large amounts in the diets of young pigs (Renaudeau, personal communication).
Fresh foliage replacing 25 and 50 % of soybean meal in a sweet potatoes and soybean meal diet resulted in a decreased of dry matter intake that was probably due to its bulkiness, but the feed conversion ratio was conserved at the 25% replacement level (Göhl, 1982).
Gilts and sows
Sweet potato leaves inclusion can be as high as 50% in the diets of gilts or pregnant sows, and up to 20% for lactating sows. They can also replace up to 50% soybean meal during pregnancy and lactation (Hoang Nghia Duyet et al., 2010; Hoang Nghia Duyet, 2003).
Preserved sweet potato foliage
Sweet potato foliage in fresh, dried or silage is a valuable ingredient for pig diets. Though dried and ensiled sweet potato foliage have slightly lower lysine digestibility, the three products have similar palatability and overall nutritive values (Le Van An et al., 2004).
Many types of silages can be done with sweet potato foliage: sweet potato silage can be prepared with leaves alone or in mixtures: leaves and lysine, sweet potato leaves and cassava leaves, sweet potato leaves and sweet potato roots (Nguyen Thi Hoa Ly et al., 2010; Le Van An et al., 2005). Ensiled cassava leaves and sweet potato vine can replace more than 70% of the protein from fish meal (or 35% of total diet CP), reducing feed costs without deleterious effects on growing pig performances or carcass quality. (Nguyen Thi Hoa Ly et al., 2010). 30% inclusion rate for ensiled sweet potato foliage should not significantly affect growth performance in growing pigs (Le Van An et al., 2005). Higher inclusion rates (40 and 60% DM) would reduce growth by 16 and 30%, respectively (Hoang Huong Giang et al., 2004).
In post-weaning diets, sweet potato inclusion (meal or silage) should not exceed 10% and to 30-40 % inclusion is advisable in growing-finishing diets (Mora et al., 1992 cited by Le Van An et al., 2005).
Dried sweet potato vines can be used in poultry rations as a source of protein and carotenoids, particularly beta-caroten and xanthophylls, and have been included in diets to enhance the yellow pigmentation of broiler skins and egg yolks. Early-harvested vines were as efficient as alfalfa meal at colouring yolks. Late-harvested vines were less efficient at colouring broiler skin (Woolfe, 1992). An optimum level of 10% has been suggested, as higher levels resulted in decrease of dry matter intake and body weight gain (Berhan Tamir et al., 2010) and levels of 20-30% reduced the feed conversion efficiency (Kagya-Agyemang et al., 2008). However, dried vines included at up to 16% in broiler diets have been shown to be as efficient as alfalfa meal for growth rate, food intake or food efficiency (Farrell et al., 2000) and 15% could be economically feasible if birds are sold if birds are sold on eviscerated carcass weight basis rather than live weight (Wude Tsega et al., 2009).
Fresh sweet potato leaves given to chickens gave the smallest animals, the highest mortality and the lowest economic results when compared to fresh leaves ofcentro (Centrosema molle) and leucaena (Leucaena leucocephala) (Dingayan et al., 1950).
Sweet potato vines are palatable to rabbits and have been found to be more palatable that Leucaena leucocephala and other legume trees (Raharjo et al., 1985). In rabbits fed a concentrate diet, fresh sweet potato vines resulted in a slightly lower intake and daily gain (21.1 g/day) than water spinach (Ipomoea aquatica). The best performances were obtained when adding Guinea grass (Megathyrsus maximus) to sweet potato vines, water spinash or a mixture of both forages, though the digestibility of the diets was lower (Doan Thi Gang et al., 2006). Groundnut haulms and soybean forage were more cost effective than sweet potato forage for feeding rabbits (Iyeghe-Erakpotobo, 2007).
Sweet potato leaves have been used to feed Tilapia in Ugandan fish ponds (Mwanga et al., 1988). In Vietnam, sweet potato crop residues and other macrophytes have been tested successfully for feeding Tilapia, common carps (Cyprinus carpio), giant gouramis (Osphronemus goramy) and kissing gouramis (Helostoma temminckii) (Lam My Lan et al., 2007). Sweet potato leaves were assessed to be suitable for small scale freshwater fish feeding (carps and Tilapia) due to their relatively high protein content and reduced antinutritional factors (Dongmeza et al., 2009).
When farmed crayfish (Procambarus clarkii) were fed vines and root trimmings from a sweet potato cannery as a supplement, dried sweet potato foliage fed ad libitum daily resulted in the highest weights and longest lengths of mature crayfish, followed by sweet potato trimmings, rice stubble and rye hay. Sweet potato vines and trimmings could be fed directly to crayfish or after a very short compost period. Fresh sweet potato forage was more efficient than forage stored in water, which may be due to unpalatable decomposition products (Goyert et al., 1977).
Tables of chemical composition and nutritional value
|Dry matter||% as fed||13.0||2.9||8.5||17.6||21|
|Crude protein||% DM||16.5||4.6||8.2||24.2||23|
|Crude fibre||% DM||21.1||5.3||11.9||30.3||17|
|Ether extract||% DM||4.8||2.0||2.5||10.4||14|
|Gross energy||MJ/kg DM||18.3||*|
|Glutamic acid||% protein||7.9||1.2||6.4||9.6||5|
|Tannins (eq. tannic acid)||g/kg DM||6.2||1|
The asterisk * indicates that the average value was obtained by an equation.
Bui Phan Thu Hang et al., 2011; CIRAD, 1991; Devendra et al., 1970; Dominguez, 1992; Dongmeza et al., 2009; Hassoun, 2009; Holm, 1971; Le Thi Men, 2006; Luh et al., 1979; Nguyen Nhut Xuan Dung et al., 2002; Pozy et al., 1996; Teguia et al., 1993; Thim Sokha et al., 2008
Last updated on 24/10/2012 00:45:13
|Dry matter||% as fed||88.5||3.3||84.0||92.6||10|
|Crude protein||% DM||13.2||6.0||7.6||21.7||11|
|Crude fibre||% DM||19.9||4.7||12.2||23.7||7|
|Ether extract||% DM||2.8||1.3||1.0||5.4||9|
|Starch (polarimetry)||% DM||1.8||1.2||2.3||2|
|Total sugars||% DM||7.9||6.7||9.0||2|
|Gross energy||MJ/kg DM||17.5||0.9||16.8||18.9||4||*|
|Aspartic acid||% protein||9.4||1|
|Glutamic acid||% protein||10.0||1|
|Ruminant nutritive values||Unit||Avg||SD||Min||Max||Nb|
|OM digestibility, Ruminant||%||66.0||1|
|Energy digestibility, ruminants||%||61.8||*|
|DE ruminants||MJ/kg DM||10.8||*|
|ME ruminants||MJ/kg DM||8.8||*|
|Nitrogen digestibility, ruminants||%||33.0||1|
|Pig nutritive values||Unit||Avg||SD||Min||Max||Nb|
|Energy digestibility, growing pig||%||42.5||38.5||46.4||2|
|DE growing pig||MJ/kg DM||7.4||6.6||7.4||2||*|
|MEn growing pig||MJ/kg DM||6.8||6.5||6.9||2||*|
|NE growing pig||MJ/kg DM||4.1||*|
The asterisk * indicates that the average value was obtained by an equation.
Last updated on 24/10/2012 00:45:27
|Aspartic acid||% protein||9.1||1|
|Glutamic acid||% protein||11.3||1|
The asterisk * indicates that the average value was obtained by an equation.
Last updated on 24/10/2012 00:45:35