Silage fermentation requires an anaerobic environment. So the pre-requisite condition for fermentation is to eliminate as much as possible the air from the fermenting material. Chopping the material ensiled, and the pressure exerted on the chopped material inside the containers where silage fermentation will occur, favor the elimination of most of the air present between the plant particles. Under these circumstances it is expected that anaerobic fermentation will start a few hours after the silage has been sealed; therefore losses due to transpiration and the activity of non-desirable aerobic microorganisms (e.g. enterobacteria, molds) will be minimal.
Ensilage should take place in completely air-tight nylon or plastic bags to make sure that no air can enter and spoil the silage.The exposure of the silage to air is unavoidable once the bag is opened for feeding animals, and it results in deterioration of the product. One way to reduce those losses is to use a high feed-out rate of the silage, which is obtained by working in relatively small batches, which can be completely consumed at most in 7-10 days after opening the silage. In small-scale exploitations, the use of bags for ensiling is quite adequate for this purpose, as silage contents can be consumed almost the same day, and then this type of loss is minimized.
• Reducing the moisture content of the ensiling material
Because sweetpotato vines have high moisture content (up to 90% water), it is necessary to pre-wilt them before fermenting. Otherwise there is not only the risk of loosing nutrients by excessive effluents coming out from the silage or the loss of all silage soaked in water when drainage is impeded, but also the possibility of Clostridia development in the silage, resulting in poor quality silage (high in butyric acid, most of the protein degraded to ammonia).
• Using additives for ensiling
Several additives can be used to improve the ensiling process, but those can be classified as fermentation stimulants (e.g., inoculants, molasses), fermentation inhibitors (e.g., formic acid, mineral acids, salt), aerobic deterioration inhibitors (e.g. propionic acid), nutrients (e.g., urea, minerals) and absorbents (e.g., straw, dried sugar beet pulp).
Sweet potato vines practically contain all nutrients required for a good fermentation process, except for its high moisture content, which can be controlled by pre-wilting. However, in many practical experiences good results have been obtained using corn meal, cassava meal, rice bran, chicken manure and salt. The main effect of the first four could be as absorbents, given their high dry matter content, whereas salt restricts fermentation, preventing a large proportion of available non-structural carbohydrates from fermenting. In the case of chicken manure, the ammonia released during fermentation may also help to improve the aerobic stability of the silage, once the silage is opened.
For ensiling sweet-potato roots, it is even more necessary to use additives with high dry matter content, as roots cannot be pre-wilted. Also, the low protein content of sweet-potato roots may limit the growth of fermenting microbes; therefore the use of protein rich additives (e.g., chicken manure or even urea) may help. The use of salt as an additive is particularly relevant in the case of roots, as it could help to save some of the starch and sugars from being fermented in the silage. The quality of the fermented sweet-potato vines and tubers can be kept stable for a long time if processed properly.
1.1.2 Ensiling sweetpotato vines
Sweetpotato vines are converted to silage by the following procedure:
• Chopping sweetpotato vine
Chop SP vine to 0.5-1 cm length, remove the old, yellow and rotted leaves
Pre-wilting is a very important step to reduce moisture content of fermenting material.
After chopping it needs to be partially wilted immediately in the sun until the water loss is about 40-45 %. For example: if you have 100 kg of fresh SP vine, after pre-wilting the water loss is 40-45 kg remaining pre-wilted SP vine is about 55-60 kg.
Try the following: hold the wilted SP vine in your hand then open the hand. If the SP vine keeps the * initial shape, the wilting is enough. Pre-wilting can take about 2-4 hours in dry, sunny weather. During pre-wilting the vines should be turned over regularly to allow rapid and uniform wilting.
You should harvest the amount of SP vine that is just enough to chop,
pre-wilt and ferment on the same day to minimize nutritive loss.
After pre-wilting, sweetpotato vine is gathered and left to cool down. Then the materials are weighed and combined based on the proportions of the formulas below:
Formula 1: 93.5 % pre-wilted SP vine + 0.5 % salt + 6 % cassava meal (or 6 % corn meal or 6 % rice bran)
If you have chicken manure, use the following proportion:
Formula 2: (83.5 % prewilted SP vine + 0.5 % salt + 6 % cassava meal (or 6 % corn meal or 6 % rice bran) + 10 % dried and ground chicken manure
• Mixing and ensiling
Rice bran or chicken manure Sweetpotato vine
The weighed materials are mixed together by hands or by hoes. To be sure that the very little amount of salt is mixed evenly, first it is mixed with the additive(s) then mixed with pre-wilted SP vine.
The bags containing the fermented feed need to be kept in a dry, cool place and avoid mice and insects. The bags would become aerobic when bit or scratched by them; consequently, the feed would mold or rot.
Remark: Check the bags during the first and second day after fermenting. If there is air in the bags, open the bag to let the air out then close tightly again. This air is generated by the transpiration of SP vine or roots.
1.1.3 Ensiling sweetpotato roots
The procedure of ensiling sweetpotato roots is as follows:
• Grating, chopping or slicing sweetpotato root
Grate, chop or slice SP root as small as possible. Remove the rotted
or weevil-attacked parts of the roots, or discard the whole root if well
damaged. Ensiling should be done as soon as enough sweetpotato roots have
Weigh the grated or chopped SP root and the additives according to the proportion of the formulas below:
Formula 3: 79.5 % SP root + 0.5 % salt + 20 % rice bran (or cassava leaf meal)
If you have chicken manure, use the formula below:
Formula 4: 79.5 % SP root + 0.5 % salt + 20 % dried, ground chicken manure.
• Mixing and ensiling
• Packing the bags (refer to methods for packing fermenting SP vine).
1.2 Using sweetpotato vine and root silage to feed pigs
• How many days after ensiling can we start using ensiled sweetpotato vine and root to feed pigs?
If sweetpotato vines are ensiled according to formula 1 (with rice bran or com meal or cassava meal and salt), it can be fed to pigs at 14 days after ensiling. If sweetpotato vines are ensiled according to formula 2 (with rice bran or com meal or cassava meal and salt and chicken manure), it should wait until 21 days after ensiling.
If sweetpotato roots are ensiled according to formula 3 (with rice bran or cassava leaf meal and salt), it can be fed to pigs at 14 days after ensiling. If sweeetpotato roots are ensiled according to formula 4 (with chicken manure and salt), it should wait until 30 days after ensiling.
The proposed period of time is needed for the pH value to become stable. Under this management, the quality of the ensiled feed is good and stable and there is no risk associated with pathogens.
• Which pigs can be fed with silage made of sweetpotato vines and roots?
Fattening pigs from 18-20 kg live weight (or after the age of 2-2.5 months) can be fed with SP vine and root silage because by this time the physiology and functions of the digestive tract have been completed and become stable, so there would not be disturbances from eating fermented feeds.
Besides this, sows, including nursing sows, can be fed with sweetpotato vine and root silage but small piglets under the age of 2-2.5 months should not be fed sweetpotato vine and root silage.
• How long can fermented SP vine and root silage be stored?
It depends on anaerobic conditions. If it is the most anaerobic (well
pressed, air tight closed, no hole, no scratches), it can be stored for
at least 4.5-5 months with no significant nutritive value reduction.
Sweetpotato vine and root silages are mixed with concentrates according to Section 3 of this chapter.
When sweetpotato vine and root silage are offered the first time, animals must learn to adapt to these new diets including the silage.
• How to adapt
For the first 2-3 days feed pigs only twice per day (early evening and late morning), and reduce the amount of feed so that pigs are hungry. This way they will have to eat new feeds and get acquainted with the new diet faster, and this helps to reduce the adaptation period. The amount of new feed should be increased gradually, so this can take one week. One should be strict in getting pigs acquainted with the new diet.
The silage made of sweetpotato vines or roots, fresh chopped SP vine and the base feed (commercial concentrates) are weighed or estimated according to the rations for each growing stage (i.e., live weight categories) of pigs. The daily ration formulas are provided later in the chapter. Feeds are mixed together with some water and fed uncooked (raw) to pigs. In winter, water should be heated. The daily feed ration should be divided into three meals to feed pigs in the morning, in the afternoon and in the evening. Feeding in this way is simple, convenient and economical because no fuel, time, or labor is needed to cook the feed.