Cassava Wastes as Feedstuff 4: Feeding value of cassava leaves in animal nutrition

Published Date 29th June 2020

Considerations in formulating cassava leaf-based diets

The cassava leaf is a good source of protein, carbohydrate, vitamins, and minerals for livestock. It can be used as silage, dried for feed supplementation, and processed into leaf protein concentrate for the improvement of high fiber feedstuffs. Cassava leaf can also be processed together with the stem and used as pig, poultry, dairy cattle, sheep, and goat feeds, or dried for feed concentrates. The meal produced from the leaves although high in protein is deficient in methionine, isoleucine, and threonine. The amount of protein in the meal also depends on the stage of growth.

The major problems that limit the potential of cassava leaf as an unconventional protein resource for animals are however the high fiber content and the presence of anti-nutrients like cyanide, tannin, and phytin. The different techniques developed by scientists to reduce or eliminate these anti-nutrients were discussed in the previous blog. Demonstrated inclusion levels of processed cassava leaf products however remain relatively low for most non-ruminant animal diets, chiefly because of the high fiber and other limiting anti-nutrients. Progress in research is expected in the near future to result in the development of better cassava leaf products that would be used to achieve higher dietary replacement levels of the costly conventional protein sources in order to sustain the current growth in tropical livestock production.

The nutritive value of cassava leaf meal for poultry

Several studies have attempted incorporating cassava leaf meal as a feed ingredient or substitute for other ingredients in the diets of different classes of poultry. The available literature shows that cassava leaf meal could be used successfully as a protein source in poultry diets. The level of inclusion in poultry diets will however depend on the type of ingredients that are being replaced. Asian studies have shown that as a substitute for coconut meal or cottonseed meal, cassava leaf meal can be used up to levels of 10 - 15 g kg-1 with no adverse effects on performance. However, the inclusion of cassava leaf meal beyond the 5 g kg-1 level in maize-soybean diets was not recommended unless the diets were supplemented with energy and methionine. The unfavorable effects of high dietary levels of cassava leaf meal are due to bulkiness, reduced energy intake, and methionine deficiency. Thus, the growth depressing effects at high levels of inclusion could be alleviated by supplemental methionine, and energy, and by pelleting the diets.

Recent Nigerian studies revealed that the final body weight of broilers was significantly reduced and feed intake was increased when cassava leaves replaced more than 50 percent of dietary maize. A combination of 20 percent each of cassava leaf meal and cassava peelings was able to replace maize and soybean meal in broiler diets, without affecting performance. In an interesting recent study, researchers at the University of Abuja, Nigeria, partially replaced groundnut cake with cassava leaf meal, with or without enzyme supplementation in the diets of broiler starter chicks. They reported superior final weight of birds fed cassava leaf meal with or without enzyme supplementation up to 40 percent inclusion level. Researchers at the University of Agriculture Abeokuta, Nigeria, fed diets containing cassava leaf meal and blood meal mixtures to broiler chicks as a replacement for soybean meal. The birds fed the diet containing 50 percent soybean meal: 50 percent cassava leaf/blood meal mixture recorded the best weight gain, feed intake, and feed conversion ratio.

It is recommended that the maximum level of cassava leaf meal to be used in the diets of laying birds should be 5 to 6 percent, to minimize the effects of the low palatability of such feeds. In addition, beyond these levels, the energy balance of the diets cannot be guaranteed. Cassava leaf meal can be added to cassava root meal-based layer diets to supply the carotene needed to maintain yolk color. Studies with Cambodian and Pekin ducks however established that cassava leaves can be included up to 15 percent in duck diets without affecting growth rate or feed conversion. It was also observed that the weight of the digestive system of these ducks increased with increasing dietary cassava leaf meal content. Again, feeding cassava leaves and chips to guinea fowl has no negative effects on feed conversion ratio but help to reduce feed cost per kg live weight gain by about 25 percent compared to the control group.

The nutritive value of cassava leaf meal for pigs

Early studies on feeding fresh cassava leaves to pigs showed that palatability was depressed, and growth performance was lowered with increasing proportions of cassava leaves in the rations. It was however established that fresh cassava leaves could form up to 150 g Kg-J of the dry matter intake with no adverse effects on the performance of growing-finishing pigs. Ravindran in his classical study substituted 100, 200, and 300 g kg-1 cassava leaf meal for a corn-soybean meal-basal diet and reported that gains and feed efficiency of growing pigs were depressed linearly with increasing levels of leaf meal. The performance of pigs on diets containing 100 g kg-1 cassava leaf meal was however improved by methionine and extra energy supplementation. Cassava leaf meal as a substitute for coconut meal has also been evaluated with the results showing that the meal, prepared using a combination of chopping, wilting and sun-drying, can replace up to 660 g kg-1 of coconut meal in growing pig diets without adverse effects on performance. Some researchers reported depressions in weight gain and feed efficiency when cassava leaf meal was included at 200 and 300 g kg-1 levels in diets for growing-finishing pigs.

Cassava leaf meal has also been used to partially replace peanut meal, fish meal, and corn in the basal ration, with adverse effects reflecting the high levels of residual cyanide in the meal, thereby emphasizing the importance of proper processing. Investigators at the University of the South Pacific, Apia, Samoa, evaluated the effects of cassava leaf meal protein in fish and soybean meal-based diets for young pigs and reported that it is possible to replace 30 percent of feed protein with sun-dried cassava leaf meal protein in such diets without adverse effects on their growth performance, and helped to reduce dependence on expensive feed resources.

Processing cassava roots and leaves by ensiling are easier than sun-drying, especially during the wet season in tropical countries. Research reports from the Hue University of Agriculture, and Forestry, Vietnam, showed that cassava leaves could be ensiled with rice bran or cassava root meal at levels of 5 or 10 percent, and fresh cassava roots at levels of 20, 30, 40 and 50 percent, resulting in good quality silage that could be stored for at least five months. The dry matter and crude protein contents of the end products for all additives ranged from 26.42 to 32.98 percent and 19.79 to 27.52 percent respectively, 90 days after ensiling. Hydrogen cyanide content of the products decreased very rapidly from the first day to 30 days and then continued to decrease from 30 to 90 days so that the value was only about 20 – 28 percent of the original value at 90 days after ensiling. Feeding trials at this study location showed that inclusion of 13 – 15 percent of ensiled cassava leaves in rations that contained 30 percent ensiled cassava root as a replacement for sweet potato vines, and partial replacement of fish meal in diets of growing pigs did not affect the growth rate but reduced the feed cost/kg gain by 12 to 26.8 percent. Similarly, supplementation with 0.1 percent methionine in the diets containing 30 percent ensiled cassava root and 15 percent ensiled cassava leaves improved the performance of growing pigs.

In Cambodia, scientists studied the effect of graded levels of refined palm oil introduced in diets of broken rice and ensiled cassava leaves to evaluate nutrient digestibility in pigs. The cassava leaves were ensiled with 5 percent of sugar palm syrup for 30 days in plastic containers to produce silage of 50.7 percent dry matter, 14.1 percent ash, 85.9 percent organic matter, 35.3 percent crude fiber, 47.0 percent neutral detergent fiber, and 3.92 percent nitrogen on a dry basis, while the cyanide content was 110 mg/kg.

The nutritive value of cassava leaf meal for ruminants

Cassava foliage could also be satisfactorily preserved as silage for use as a dry season feed for ruminants. The leaves are particularly suitable for rural farmers because they are available in large quantities during cassava harvest. The major challenge to using cassava leaves in the ruminant diet is their low levels of neutral detergent fiber (NDF), and a high level of hydrogen cyanide, which usually results in low weight gain. Supplementing cassava leaf meal-based diet for ruminants with high NDF sources such as grass and rice straw is one method of increasing NDF in the diet. Cassava peels have also been combined with cassava leaves and cowpea haulms in the diets of small ruminants to achieve the same purpose. Ruminants are more susceptible to hydrogen cyanide poisoning because the rumen microflora produces enzymes that act on cyanogenic glucoside in the cassava leaf to release the poisonous hydrogen cyanide into the bloodstream. In most cases, chronic poisoning is observed in the herd as a result of the continuous intake of small amounts of cyanic acid over long periods of time.

Researchers at Jimma University, Jimma, Ethiopia, investigated the effects of supplementing cassava leaf meal, brewers’ dried grain, and their mixtures on body weight change, and carcass traits of local goats fed urea treated tef straw. The experiment consisted of four ad libitum feeding of urea treated tef straw as control and supplementation with 300 g cassava leaf meal, 150 g cassava leaf meal +150 g brewers’ dried grain, and 300 g brewers’ dried grain. They reported that the goats fed the two cassava leaf meal supplemented diets performed better than the other groups in terms of final body weight, and average daily gain, thus highlighting the positive potential of cassava leaf meal as a good supplement for ruminants on a basal diet of fibrous feed. Another study at the University of Agriculture, Makurdi, Nigeria, have also shown the optimum cassava leaf meal inclusion level in a basal diet of rice straw and maize offal (70 percent maize offal:30 percent dried cassava leaf meal; 50 percent maize offal:50 percent dried cassava leaf meal; 30 percent maize offal:70 percent dried cassava leaf meal) to be about 20 percent of the dry matter intake.

Conservation of excess cassava leaves available during cassava root harvest period through silage making, in order to maximize the efficiency of the leaf utilization as feed is a common practice in some Asian countries like Indonesia. As silage, the excess cassava leaves are preserved and utilized for longer periods of time as a protein feed supplement for ruminants.  Feeding cassava leaf silage has been reported to enhance livestock productivity, in terms of milk yield and body weight gain. Researchers at the Brawijaya University, Malang, Indonesia, investigated the use of cassava leaf silage as a feed supplement for sheep fed on elephant grass. The cassava leaf silage was supplemented at 0, 0.75, and 1.5 percent, which represented a 5 percent body weight total dry matter intake. They reported significant improvements in average daily weight gain from 41.4 to 45.0 and 50.0 g/head/day in the animals fed the cassava leaf silage. Thus, mixing cassava foliage with roughages improves fermentation and increases the protein content of the silage. However, the energy utilization of such silage is usually lower than that of cassava foliage hay.

Dry season feeding has become a critical factor in the sustenance of pastoral cattle production in any part of Africa as grazing lands continue to shrink because of the increasing human population, urbanization, and other anthropogenic activities. Dry season fodder is usually poor in nutrient quality and cannot sustain animal conditions and reproductive needs during the long dry season months, thus the need for supplementation with feeding materials from elsewhere. During this period, there is a high demand for both quantity and quality fodder, especially for productive ruminants such as dairy cattle. Cassava hay containing a high level of crude protein (25 percent) and low levels of fiber can serve as a high nutrient supplement for ruminants in the traditional grazing zone during this period. Cassava leaves can be gathered after root harvest, and sun-dried for 3 - 5 days before being collected in bundles or made into a square bale prior to feeding or storing for later dry season feeding. A short drying period of 2 - 3 days has been advocated in order to secure leaf attachment and higher quality, while longer drying periods of 4 - 6 days may be necessary for drying the stem, and branches that are higher in moisture content. Sun-drying does not only reduce moisture but also helps to decrease hydrocyanic acid to a safe level for ruminants.

Studies at Khon Kaen University, Khon Kaen, Thailand, have demonstrated the high protein, digestible nutrient contents, together with a high consumption rate of cassava hay by cattle, indicating that it is an excellent feed either for full feeding as cassava hay or as a supplement in crop-residue based diets, such as urea-treated straw, and sugar-cane tops. Thus, a strategic feeding system based on importing quality cassava hay from the southern cassava producing belts of West Africa to the pastoral north for augmentation of shortfalls in local fodder production during the dry season months could be implemented to sustain ruminant livestock production in the sub-region.

Conclusion

Much progress has been made through research in exploiting the cheap, and readily available cassava leaves for livestock feeding in the tropics. The nutritive values of the differently processed cassava leaf products are continually being researched at different tropical locations with promising results. It is, therefore, now possible for farmers to utilize these products as partial replacement of conventional feedstuff in the feeding of poultry, pigs, and ruminants, in order to save cost, and limit the practice of feeding food crops to livestock.

Bibliographic References

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