Making sweet silage for pigs from potato vines

While cattle and sheep graze, goats browse and indigenous chicken scavenge for food, pigs are legally raised in confinement as a control measure against African Swine Fever (ASF).

The simple stomach nature of pigs makes it necessary to feed them on commercial feeds that consume 60-80 per cent of production costs.

Therefore, one needs affordable and highly nutritious feeds that supplement the commercial ones to raise profit in pig farming. Such feeds include sweet potato tubers and vines, which can be used fresh, dried or fermented into silage.

In addition to conserving the otherwise highly perishable tubers and leaves during peak production for use when there is scarcity of feeds, ensiling enhances the quality of the feed material by converting nitrogen to protein. Sweet potato silage has been used successfully to raise pigs in many countries.

Pig feed

Energy and protein are the main nutrient components in a pig’s diet. Grains such as maize, barley, wheat, sorghum and oats have traditionally supplied energy, while protein has come from meals produced from oilseeds such as soybeans and canola.

Issues to consider in pig feed production include palatability, quality and costs which will arise from feed loading and offloading labour and transport especially if feeds are bulky.

Palatability is the extent to which an animal likes to eat a certain feed. Inclusion of certain materials affects palatability at various stages of pig growth. Further, some ingredients might have anti-nutritional factors that interfere with the feed palatability and utilisation.

However, processing some of the feed inactivates anti-nutritional factors. For example, raw whole soya beans contain an anti-nutritional factor that inhibits utilisation of the trypsin enzyme resulting in decreased palatability and use.

But heat processing inactivates the anti-nutritional factor. Other ingredients that contain anti-nutritional factors include canola, lupins and potato chips.

In countries like China, recent estimates indicate that as much as 65 per cent of sweet potato production is for animal feed production.

Although Kenya has increased sweet potato production in the recent past, its utilisation for animal feed especially pigs is still low.

The crop is drought-resistant and the tuber and leaves are palatable and highly digestible. To plant sweet potato fodder, dig hills of soil 15cm deep, cut vines of about 30cm long and burry three-quarters in the soil.

The vines will need a handful of manure per hole and fertiliser at the rate of 60kg per hectare. Spacing is 30x60cm and the seed rate is 4,000 or more pieces per foot long per acre.

The plant matures in three to four months and yields five to six tonnes of fresh vines per acre. Cutting interval is two to three months depending on the weather.

The vine’s crude protein (CP) is 12 — 15 and dry matter content is 22 per cent. Optimise quality by making silage, which is a way of preserving the material in an oxygen-free environment.

Making sweet potato vine silage

Harvest and wilt the vines for three days in a partial shade then chop them into 5-1cm long pieces. Chop tubers into 2.5cm2 pieces and place the contents in alternating layers into a silage bag, drum or pit at the rate of 70 per cent vines, 30 per cent tubers and 0.5 per cent salt or sun-dried poultry manure. A 95 per cent vine and 5 per cent maize bran can replace the sweet potato root content.

Mix each layer thoroughly. Firmly compress each layer by rolling on it a heavy object such as water filled drum. Cover the compacted material with a thick layer of black polythene to exclude air and water and cover the later with some soil logs or stones to keep the paper in place.

Make 10cm slits at the bottom of the silage tube to enhance effluent drainage. The silage will be ready for utilisation after 30 days.

Feeding

The silage is best fed to pigs that are over three months of age and weigh more than 25kg. A pig consumes about 3-6 per cent of its body weight per day and 40 per cent of this can come from the silage and 60 per cent from pig feeds (concentrates).

Estimate the feed requirement, weigh and feed the concentrate first, then give the pigs as much silage as they can consume.

The writer is a livestock expert. [email protected]

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Pigs can feed on leftovers

• Pigs eat all kinds of leftover foods.
• These include bread, ugali, vegetables and fruits.
• However, experts recommend commercial pig pellets as the best feeds.
• Do not only feed one feed for instance vegetables such as cabbage, because they need varied diet.