Making use of sweetpotato vines as silage

When James Francis Ojakol enrolled for a Master degree in animal science at Makerere University, he had no idea how he would finance his studies nor what area to study.

An opportunity from International Potato Center (CIP) to fund a research project fell into his lap.
Uganda is hosting a three-year $4m (Shs13.4b) project, funded by the European Union, which will expand the utilization of roots, tubers and bananas and reduce their post-harvest losses. The project is part of the CGIAR Research Program on Roots, Tubers and Bananas, of which CIP is the lead center.

Among other things the project will improve utilisation of sweetpotato vines, roots and peels as pig feeds in Uganda, said Diego Naziri, a post-harvest specialist at CIP in Uganda and the leader of the project.

Quality animal feed
Ojakol is now engaged in a two-year research that will contribute to this project. His topic is ‘Evaluation of Sweetpotato Silage as a Basel Diet for Growing Pigs’.

“The general objective is to improve pig production in Uganda through the use of sweetpotato silage as a low cost and high quality feed,” he says.

Research has already established that sweetpotato is a good feed for animals and livestock and specifically pigs. Ojakol’s research is of utmost importance to farmers in Uganda for many reasons. Research shows that feeding costs for pigs represent about 70 per cent of the variable costs in smallholder farms.

Pigs in Uganda feed on sweetpotato silage. Photo S.Quinn/RTB

Pigs in Uganda feed on sweetpotato silage. Photo S.Quinn/RTB

Indeed, women and the youth will benefit more from Ojakol’s research and the silage technology most since they are more responsible for pig management at a household level. Silage will reduce the time for sourcing feeds and reduce on the use of fuel like firewood for cooking them.

“Women are participating more in growing sweetpotatoes and in keeping pigs. Of course, unfortunately, they have the challenge of feeds, so they can’t keep a lot,” notes Gerald Kyalo, the principal investigator of the project.

“If we can get these women to make silage, that means they can increase the number of pigs they are keeping and of course that then will increase income.”

Prevent wastage
Uganda ranks number one, in East Africa, in pork per capita consumption. In Uganda, 44 per cent of farmers grow sweetpotatoes but the vines are discarded after harvesting and left to rot in the gardens.

A farmer with sweetpotato silage he has prepared for his animals, Uganda. Photo S.Quinn/RTB

A farmer with sweetpotato silage he has prepared for his animals, Uganda. Photo S.Quinn/RTB

Yet they can be ensilaged and used as pig feed during the dry season when there is feed scarcity.
Sweetpotato is the third most important food crop after cassava and bananas in Uganda. In Africa, Uganda is now the leading producer of sweetpotato only second to China in the world. However, simple technologies like ensilaging have not yet been embraced.

The simple affordable technology of ensilaging the roots and vines will help to prevent wastage of valuable feed resources, adds Kyalo.

Sweetpotato is seasonal. There are times after harvesting that farmers have a lot of sweet potatoes and during harvesting they waste all the vines. Yet these same farmers have pigs. So, during times of scarcity like during the dry season, they really have nothing to feed the pigs.

“Our objective is to bridge the gap of feed scarcity especially during the dry season. We are introducing silage making to farmers, teach them how to make silage of good quality, how to supplement it, and how to feed their pigs. This will bridge the gap of lack of feeds and actual expensive feed,” observes Kyalo.

Potential benefits
“The processed sweetpotato residues offer an inexpensive and nutritious alternative feed ration for livestock that may increase economic returns,” Dr Jolly Kabirizi, a researcher at the Ugandan National Livestock Resources Research Institute, points out. The roots are a good source of energy and the vines a source of protein but they are highly perishable.

Kabirizi said sweetpotato has potential benefits to poor farm households and urban consumers especially when other crops fail or in specific seasons before the main harvest.

Ojakol’s research has three specific objectives; to determine the quality of silage prepared from sweet potato vines, the nutrient digestibility of sweetpotato silage in growing pigs and to determine the growth performance of pigs fed on sweet potato silage.

The research has four arms: the control is the commercial diet with pigs fed on a mixture of maize brand, omena and cotton seed.

Others are fed on ensilaged sweet potato vines mixed with five per cent maize brand; ensilaged sweet potato vines mixed with five percent cassava flour and ensilaged sweetpotato vines only.
“Our intention is, first of all, to get the right ratios for silage. And I think we are already making progress with the research on the station,” says the principal investigator Kyalo.

He adds they also want the farmers they have trained to take up silage making as a business.
Many of the places, Masaka and Kamuli, have a lot of sweetpotatoes and can easily start selling silage.


A field of sweetpotato growing in Uganda. Photo S.Quinn/CIP

Silage is made in a vacuum. When you open it, it can stay for 10 days, according to Kabirizi. You can make several drums and open them one at a time.

Ojakol spends most his study time at Kamenyamiggo Satelitte Station, which is under Naro’s Mukono Zardi, where the research is taking place. He has to make the silage and he keeps on recording the weight gain for the pigs. For Ojakol the timing has never been better. “We have no doubt that Ugandan pigs will like silage and farmers will sell it and benefit from it too,” he says with a smile.

The principle of silage making
At harvest, plant cells do not immediately “die”; they continue to respire as long as they remain adequately hydrated and oxygen is available. The oxygen is necessary for the physiological process of respiration, which provides energy for functioning cells. In this process, carbohydrates (plant sugars) are consumed (oxidised) by plant cells in the presence of oxygen to yield carbon dioxide, water and heat: sugar + oxygen = carbon dioxide + water + heat.

Once in the silo, certain yeasts, moulds and bacteria that occur naturally on forage plants can also reach populations large enough to be significant sources of respiration. In the silage mass, the heat generated during respiration is not readily dissipated, and therefore the temperature of the silage rises.

Although a slight rise in temperature from 80° to 90°F is acceptable, the goal is to limit respiration by eliminating air (oxygen) trapped in the forage mass. Some air will be incorporated into any silo during the filling process, and a slight increase in silage temperature is likely. These temperature increases can clearly be limited by harvesting at the proper moisture content and by increasing the bu k density of the silage.

Generally, it is desirable to limit respiration during the fermentation process by using common sense techniques that include close inspection of the silo walls prior to filling, harvesting the forage at the proper moisture content, adjusting the chopper properly (fineness of chop), rapid filling, thorough packing, prompt sealing and close inspection of plastics for holes.

Read the original article by Esther Nakazzi on the Ugandan Daily Monitor website

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