Use of Cassava as Animal Feed

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Studies on the processing and use of cassava tops as animal feed 

Bui Van Chinh and Le Viet Ly 

National Institute of Animal Husbandry (NIAH),
Hanoi, Vietnam 

Abstract 

Fresh cassava tops were found to have an HCN content of 863 mg/kg DM, which was reduced to 90.5 mg/kg DM after sun-drying and to 32.5 mg/kg DM after ensiling. Two studies were carried out in which the processed cassava tops were evaluated in feeding trials with growing pigs and dairy cattle. In the first experiment thirty six F1 growing pigs (local x Yorkshire) were divided into 3 dietary treatments, with 12 pigs per treatment: Control (concentrate only fed ad libitum); ECT15 (85% of the concentrate in the control treatment and ensiled cassava tops ad libitum) and ECT30 (70% of the concentrate in the control treatment and ECT ad libitum). Average daily gains for the Control, ECT15 and ECT30 pigs were 464, 455  and 442g, respectively. The feed cost of the ECT30 group was lower by 20% compared with the Control group. 

In the second study, fifteen lactating F1 dairy cows (local x Holstein) were given 12 kg brewers grains daily per head and 0.3kg concentrate per kg of milk produced.  The treatments were: ECT-UTS (11 kg of ensiled cassava tops per day and urea treated straw ad libitum);  ECT-EG (ECT ad libitum and 11 kg elephant grass per day); and ECT (ensiled cassava tops ad libitum). The milk yield was 14.5, 14.7 and 14.6 kg/day for treatments ECT-UTS, ECT-EG, and ECT, respectively. 

Key words: HCN,  ensiled cassava tops,  growing pigs, dairy cows
 

Introduction 

Cassava (Manihot esculenta) is widely cultivated in different agro-ecological areas of Vietnam. It can grow well even on the infertile soils of the upland areas. The area of cassava cultivation in Vietnam is over 250,000 ha, from which around 1,100,000 metric tons of  cassava tops is produced annually. However, casssava tops have not been widely used as animal feeds (Le Viet Ly and Bui Van Chinh 2001). Cassava tops are rich in protein, carotene and minerals, and for this reason it is considered a potential source of animal feed in tropical countries (Gohl 1993; Preston and Leng 1991; Wanapat 1997; 1999; Bui Van Chinh and Le Viet Ly 1994, 2001). One disadvantage of fresh cassava tops is that their content of cyanoglucosides (HCN) is very high, which can make fresh cassava tops unsafe as an animal feed. 

In recent years, some studies have been carried out in Vietnam on cassava top processing, in which dried cassava meal was made from fresh cassava leaves and used as  a supplement in diets for poultry and pigs. It was shown that 2-4% dried cassava leaf meal (on DM basis) can be efficiently used in laying hen and broiler diets (Duong Thanh Liem et al 1989). It was also found that ensiling cassava leaves can significantly reduce their HCN content (Bui Van Chinh 1990). When the ensiled cassava leaves replaced 30% of the protein in ”C” molasses based diets for growing and fattening pig, growth raate was still acceptable (450 g/day) (Bui Van Chinh and Le Viet Ly 1994).  

Many studies in Thailand have been undertaken to investigate the potential utilisation of cassava hay and chips as animal feed. Lactating dairy cows fed cassava hay ad libitum had similar milk yield and higher milk fat and protein compared to cows in a control group wothout cassava hay (Wanapat et al 1997, 1999). 

The harvesting time of cassava in Vietnam usually occurs at the beginning of spring when the weather is overcast and rainy, and the relative humidity is high, and it is thus difficult to dry and store cassava leaves. One alternative is the possibility of making silage from cassava tops and leaves. 

Materials and Methods 

Experiment 1. Effect of processing method on the HCN content of cassava tops 

Cassava tops (30-60 cm pieces including green leaves) were collected when harvesting the roots. They were chopped (2-4 cm) and processed by ensiling or sun drying. After 30, 45 and 60 days of ensiling or after 1, 2 and 3 days of drying the HCN content was determined. Subsequently the processing method (ensiling) that resulted in the lowest level of HCN residues with the lowest labor cost was chosen for the following experiment. 

Experiment 2.  Effect of supplementation with ensiled cassava tops (ECT) on the performance of growing pigs 

The experimental design and the composition of  the compound feed used are shown in Tables 1 and 2, respectively.

The animals were weighed at monthly intervals and feed intake was recorded daily. 

Experiment 3. Effect of feeding ensiled cassava tops on the performance of lactating dairy cows 

Fifteen Holstein*Local crossbred cows were allocated to three treatments (Table 3) over a 60 day trial period. Supplementation was with 0.3 kg concentrate per kg of milk produced and 12 kg/day of fresh Brewer's grains. The concentrate consisted of rice bran (30%), cassava meal (30%), wheat bran (20%), maize (15%), soybean meal (3%) and a mineral premix (2%).    

 
The cows were weighed at monthly intervals and feed intake and milk yield were recorded daily. Chemical composition of the milk was determined at 2 week intervals. 

Results and Discussion 

Experiment 1. Effect of ensiling or sun-drying on the HCN content of cassava tops 

The HCN content of fresh cassava tops was very high, but was reduced considerably after ensiling or drying. The HCN content was lowest (33 mg HCN/kg DM)after ensiling for 60 days and was below the safe level (less than 60 mg HCN /kg DM) officially recommended by European countries. 

The ensiled cassava tops were high in protein and could be stored for a long time because of their low pH and high lactic acid concentration (Table 5). 

Experiment 2. Effect of supplementation with ensiled cassava tops on the performance of growing pigs 

The live weight gains of the growing pigs fed 15% or 30% ensiled cassava tops (on a DM basis) were similar to those fed only the compound feed (Table 6). However, the feed cost of the group fed 30% ensiled cassava tops was 20% lower than for the group fed only on concentrates. These results show that ensiled cassava tops can replace up to 30% of the concentrate (on DM basis) in the diet without significantly reducing growth rates, and leading to considerable reduction in feed costs. 

 

Experiment 3. Effect of feeding ensiled cassava tops (ECT) on the performance of lactating dairy cows 

The daily intakes of ensiled cassava tops as a proportion of total dietary DM intake were 26.6, 34.9 and 53.6% for treatments ECT-UTS, ECT-EG and ECT, respectively (Table 7). Total dry matter intakes were similar on the three treatments.

 Milk yield and feed conversion per kg of milk produced were similar for the three treatment groups, but the feed cost per kg milk was lowest for the ECT-UTS group (Table 8). 

  

 The chemical composition of the milk was similar for the three experimental groups and was not significantly different from the milk composition before the experiment (Table 9). These results are similar to those of Wanapat (1999) in a study where cassava hay was fed  ad libitum to lactating dairy cows.
 

Conclusions 

• Ensiled cassava tops had a low HCN content (32.5 mg/ kg DM), while the content in fresh cassava tops was very high (862.5 mg/ kg DM).
• Ensiled cassava tops can replace around 30% of the concentrate in the diets (on DM basis) of growing pigs, with reduced feed costs
• Ensiled cassava tops can substitute for green grass in diets for lactating dairy cows, without reducing milk yield or quality, and decreasing the feed cost per kg of milk produced.

References 

Bui Van Chinh 1990  Study on ensiling cassava leaves and tops. Proceedings of the National Workshop on the Development of Animal Production in Mountainous Areas of North Vietnam; p: 4-7

Bui Van Chinh, Le Viet Ly, Nguyen Huu Tao and Do Viet Minh 1994  The use of sugarcane juice, “C” molasses and ensiled cassava leaves for fattening pigs. In: Annual scientific report on animal production, NIAH, Hanoi, p: 27-31

Bui Van Chinh and Le Viet Ly  2001  The use of some agro-byproducts for ruminants. Proceedings of the national workshop on nutrition and feeds for ruminants in Vietnam; p: 31-41  

Gohl B  1993  Tropical Feeds (in Vietnamese, Hanoi), p.318-320

Duong Thanh Liem 1989   Studies on the use of different kinds of leaf meal for broiler chickens. J of Agricultural  Science and Technology. Hanoi, p. 165-167

Preston T R and Leng R  A  1991  Matching ruminant production systems with available resources in the tropics and sub- tropics. p. 165-185 (in Vietnamese, Hanoi)

Wanapat M,   Pimpa O, Petlum A and Booata U 1997  Cassava hay: a new strategic feed for  ruminants during the dry season. Livestock Research for Rural Development, Volume (9) 2 http://www.cipav.org.co/lrrd/lrrd9/2/metha92.htm

Wanapat M  1999  Feeding of ruminants in the tropics based on local feed resources. p. 229-234. 

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