Promoting sweet potato as animal feed

 By JANET PANDI

SWEET potato production in Papua New Guinea is estimated to be around 3 million tonnes annually, three-quarters of which is accounted for by the highland provinces. 

About 75% of this is used for human consumption, the remaining 25% being fed to livestock. The subsistence nature of sweet potato production in the country is well reflected in that only about 1% of production, or about 30,000 tonnes, is sold at major markets around the country.  

This signifies the enormous potential to commercialise and transform sweet potato production in the country not just for human food, but for feed and industrial use. Post-harvest and marketing losses are estimated at 45-83%. This scenario not only affects the marketability of sweet potato as a fresh produce but limits its use as a processed end product.  

Another alternative to add value to this crop in order to re­duce post-harvest and marketing losses is to increase its use in feeding livestock such as poultry, pigs and fish. 

Data collected from a project funded by the Australian Centre for International Agricultural Research on improving market­ing efficiency, post-harvest ma­nagement and processing of sweet potato in PNG, indicated the major weaknesses in the sweet potato supply chain in PNG are: 

• Low value crop (per kilo) and perishable, deemed unsuitable for distant markets; 
• pricing is either by bags or by piles (heaps), arbitrary yardstick, and, 
• Poor packaging and post-harvest handling leading to significant post-harvest losses.

The strength of the sweet potato supply chain is that there are many cultivators to choose from and that this crop can be grown all year round, with no apparent seasonality.  

Furthermore, this strategic crop can be used as human food and livestock feed without threat to food security.

Based on this assessment, sweet potato can be used in a greater quantity on a regular basis as an alternative energy source in PNG.  

In terms of its use as animal feed, sweet potato can be fed to all classes of livestock. The tubers are relished by pigs and cattle and by-products of tuber processing may be fed to livestock, either in fresh form or as preserved ensiled products.  

NARI has been developing and promoting extensive uses of sweet potato in the diets of pigs, broiler chickens and layer chickens and tilapia fish to replace more expensive imported grains as sources of starch in the diets.

There are three alternative feeding strategies for alleviating the high cost of feed in developing countries. These are: 

• On-farm mixing of complete rations using purchased and locally available feed ingredients;  
• blending of a concentrate mix with whole grains or local feed ingredients, and, 
• Diluting purchased feed with local ingredients.

The three major criteria determining the regular use of these resources are: 

• Availability in sufficient quantities;  
• nutritional value must be suitable for the animals, and, 
• Prices must be competitive compared to traditional feed-stuffs.

Based on these three criteria, sweet potato has been used globally as feed for fish, pigs and poultry. In addition it has been used extensively in other industries like processed human foods such as noodles, candy, alcohol and food colorants. 

Sweet potato is ranked seventh in world crop statistics, just after cassava. Its roots are rich in carbohydrates and vitamin A and its leaves are rich in proteins. It can produce more edible energy per hectare per day than wheat, rice or cassava (Lebot 2009). 

The cost of production of sweet potato in PNG is much lower compared to that of cereal crops, due to biophysical factors, pests and sociocultural scenarios. The carbohydrates of sweet potato are highly available and can be greatly used by animals.  

The leave meal has a high protein content of between 26 to 33%, with high amino acid score. It has good mineral profile and rich in vitamins like A, B2, C and E. Apart from its nutritive values, sweet potato leaves can be harvested many times throughout the year, making the leaf meal to be abundant. 

The major factor limiting its use in monogastric animals is the presence of protease inhibitors. These substances can be inactivated by processing methods like oven or sun-drying, boiling or steaming and grinding before inclusion in animal feeds. 

Research at NARI showed sweet potato can replace up to 50% of the dry matter weight of broiler finisher ration, replacing starch supplying grains such as wheat, maize and sorghum. 

Research in other parts of the world has shown that 50% of the grain in corn-soybean diets could be replaced with sweet potato chips, without a significant depression in growth or production. With such high levels of replacement, it may be necessary to supplement such sweet potato – based diets with 0.2-0.5% of lysine. 

On-going research work at NARI showed that the performance of broiler chickens fed mashed and milled formulations of sweet potato based diets at 50 and 70% inclusion with a concentrate mix was similar and that birds were able to reach market weight of 2 kg at 42 days of age. Broilers fed on the 50% sweet potato and 50% low energy concentrate could reach market weight of 1.8-2 kg in less than 42 days, and input costs were reduced by 30%.