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Go to start Pig Feed Improvement through Enhanced Use of Sweet Potato Roots and Vines in Northern and Central Vietnam
1 Technology for growing dual-purpose and forage-purpose sweetpotato in the Northern Midlands of Vietnam
2 Technology for growing dual-purpose and forage-purpose sweetpotato in the Red River Delta of Vietnam
3 Technology for growing dual-purpose and forage-purpose sweetpotato in North-Central Vietnam
1 Sweetpotato vine and root ensiling methods and use of silage as pig feed
2 Feed crops and their processing and storage methods
3 Composition of concentrate feed mixtures (basal feed) and the rations for pigs for various weight categories
Technical supplement: Some principles of pig nutrition in the tropics


1 Sweetpotato vine and root ensiling methods and use of silage as pig feed

1.1 Method

1.1.1 Principles

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 and stems.

• Pre-wilting

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.

• Additives

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 mixture can be put into containers or nylon bags but it is best to put it in two layers of nylon bags (nylon bag inside and one sack outside). Hence, it is more convenient to feed pigs and keep the bags anaerobic during feeding. This mixture should be put in layers of about 15-20 cm. After each layer, press own hard to remove air from the materials. Close your hand as a fist and press it down hard layer by layer. Avoid scratching the bags. Immediately after finishing this work the bags are tightly closed. Remember the air must come out of the bag before closing.

• Packing the bags

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 been grated.

• Weighing ingredients

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


Mix the same way as fermenting SP vine but pack the ferment in 3 layers of bags (2 nylon bags inside and 1 sack outside) to avoid aerobic conditions or leaking. If there are lumps among the grated SP root, it is necessary to break them so that SP root particles can adhere to salt and the other additive particles.

• 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.

• Method of feeding sweetpotato vines and roots silage to pigs

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.