Sweet potato residues (vines, non-marketable roots and peels) are some of the most widely used residues as pig feed in Uganda.
One major negative attribute of sweet potatoes is that although it is a good source of energy (roots) and protein (vines), they are highly perishable.
Research conducted by the International Potato Center (CIP) and the International Livestock Research Institute (ILRI) in Uganda showed that sweet potato farmers waste on average 599 kg of vines per acre per season.
The report further indicated that all pig farmers actively engage in sweet potato production and face feed scarcity between the months of February to July.
In case of urban and peri-urban areas sweet potato residues create a disposal problem as they are dumped within the markets after sale of roots. This causes an environmental hazard.
To facilitate the use of sweet potato vines beyond the rainy season and to bridge the feed gap in the dry season, The International Potato Center; International Livestock Research Institute; Kyakuwa Farm, Wakiso district and Makerere University developed a “Sweet potato vines silage technology”.
Silage is an animal feed that is made by storing green plant material in anaerobic conditions where it is preserved by partial fermentation.
Silage making for small scale farmers using polythene tube technology
With a constant supply of sweet potato vines silage, pig farmers can triple their income for the same period through pork, pig and/or piglet sales.
This can be made possible by the use of polythene tube silage making technology. A polythene tube is good when making silage from less than 3 tonnes of fodder.
A 2.5-metre polythene tube can hold up to 500 kg of fodder.
Major steps in sweet potato vine silage making process using polythene tube technology
STEP 1: Chop, wilt and weight sweet potato residues: Chop the forage to be ensiled to lengths of about 1 inch tong using either a panga or a chaff cutter. Chop sweet potato residues (non-marketable sweet potato roots and vines) in a ratio of 1:3 (roots to vines) to be ensiled to lengths of about using a motorized forage chopper or a panga.
Chopping facilitates compaction; it releases plant juices, stimulating the growth of lactic acid bacteria and; it increases silage intake by the animal.
Longer chop lengths are more difficult to compress and displace the air within the crop especially the stems, which are harder and hence more difficult to compress resulting in losses in the silage making process. Wilt chopped sweet potato residues for 1-3 hours under the sun to reduce moisture content. Do not wilt in thick layers as the plants in the bottom will not be exposed to the sun/heat and may lead to decomposition undoing the silage making process. Weigh chopped residues and spread it on a tarpaulin.
STEP 2: Mix the material with a ferment starter: Use 10 kgs of maize bran (ferment starter) for every 100 kgs of chopped vines OR dilute 1 liter of molasses with 3 liters of water. Maize bran is suitable for fresh fodder because it absorbs some of the moisture and improves the quality of silage. Molasses provides sugar (energy) to animals, improves palatability of feed rations and aids fermentation during silage making. Molasses or maize bran increase the production of lactic acid which serves as a preservative. Spread maize bran or diluted molasses over chopped sweet potato residues and mix thoroughly OR use a watering can to distribute the solution evenly. This helps to feed the micro-organisms to make the silage acid quickly, which will prevent rotting.
STEP 3: Mix the material with microbes: Mix 0.5 litres of the microbes with 10 litres of diluted molasses and sprinkle on the vines mixed with bran or molasses.
Merits of adding microbes to animal feeds include:
(a) immune booster;
(b) increases digestibility and palatability (acceptability) of feeds;
(c) it has a good smell;
(d) improves animal weight;
(e) encourages lactic acid fermentation by inhibiting undesirable microbes and;
(f)silage matures in less than 10 days instead of the recommended 21 to 30 days.
Add salt (0.5%) to improve the taste of silage. \
CAUTION: A poor microbe production leads to diarrhoea in animals.
STEP 4: Making plastic tube silo:
Open up a polythene tubing (gauge 600-800 microns thick) and cut into pieces of 1.5 meters long for every 50-70 kg of chopped material. Pleat the black polythene tube lengthwise. The black polythene material can be obtained from all Hardware shops.
Tie firmly with a sisal twine at 30cm distance from the cut edge. Fold back the edge and tie once again to exclude the air. The container in which silage is kept is called a “silo”.
STEP 5: Place a polythene plastic tube into another 100 kg synthetic sac and fill the plastic tube with chopped material: The synthetic sac protects the polythene tube from being damaged by rodents and hot weather. Place the polythene tube silo into a- 100 kg synthetic sac
Fold the top half of the tubing over the sides of the lower part. Fill the tubing a little at a time with chopped mixed material. Every after adding about 25 kgs step over the material to compact before adding more. Take care not to tear the polythene tube. Fill until about one quarter of a meter is left. You can use plastic drums or reusable plastic silo bags. Compact the material in the bag to remove air Tie the bag firmly out as much air as possible, tie the top of the tube and place a heavy object on top to continue compacting
STEP 6: Store under shade to avoid direct sunlight damaging the polythene tube. Concrete or a wooden floor provide excellent surface for silage bags, easy removal of feed with little or no damage, can achieve exceptional drainage of water away from bags, discourages pests and makes inspection for damaged bags very easy. Rodents like rats that could tear the tube need to be controlled. Under anaerobic conditions, silage can be stored for up to 3 years.
Maintenance of sweet potato silage bags
· Number and date each bag for easy identification and recall of materials bagged.
· Do not allow dogs, cats, children and other animals to climb the bags.
· Inspect the silage bags on a regular basis and if possible and seal holes at once. If damage is extensive, the silage needs to be re-bagged as soon as possible.
· Do not leave the silage bags opened overnight.
· If maintenance is appropriate within 10 days, excellent lactic acid fermentation will result and bags kept well for six months, with no or little fungal spoilage.
· After removing the silage, the bags must be carefully washed, dried and stored in a safe place for use the following year.
Characteristics of good quality silage
· Well-preserved silage is green, yellow, or pale brown. Dark brown silage is poorly preserved.
· Well preserved silage has a sweet, tobacco smell. Foul, rancid smells indicate poor preservation.
· The silage is liked by animals because of good taste and pleasant aroma.
· No mould growth.
· Good silage is free flowing and non-sticky texture.
· Good silage has a protein content of about 18 percent.
Recommendations on feeding sweet potato vines silage to pigs:
· Farmers rearing pigs can reduce the cost of production by over 50% through adopting sweet potato vine silage technology.
· A pig consumes 3-6 percent of its body weight per day.
· Remove enough silage to feed your pigs for the whole day and tie the silage bag again to ensure air or water does not get in.
· Weigh the pig on weekly basis to know how much feed to provide.
· Sweet potato silage is best fed to pigs which are over 3 months and weigh more than 25 kgs.
· Sweet potato silage (main feed) should be supplemented with an ideal feed (supplement). The silage should comprise of 60% and the supplement 40%.
Compiled by Dr Jolly Kabirizi