Cassava as small ruminant feed in the hilly and mountainous area of Bavi district in North Vietnam 

Do Thi Thanh Van, Nguyen Thi Mui and Dinh Van Binh

 Goat and Rabbit Research Centre, Sontay, Hatay,
National Institute of Animal Husbandry, Hanoi, Vietnam

Abstract

The general aims of this review were to discuss the processing methods and the use of cassava (Manihot esculenta) as feed for small ruminants in the hilly and mountainous area of Bavi district in North Vietnam. When grown for root production the root yield is about 15 tonnes/ha and the associated leaves are 5 tonnes/ha. The crude protein in cassava leaves is in the range of  20.1 to 25.6% in the dry matter.  Sun-drying is the method of conservation used by most farmers.  

For growing goats, the mixture containing 25% dried cassava foliage, 25% dried Flemingia (Flemingia macrophylla) foliage, 11% rice bran, 11% cassava root meal and 28% molasses gave the most positive effect on the performance of the goats when fed in the ratio (DM basis) of 80% of the mixture and 20% of para grass (Brachiaria decumbens).  In diets for pregnant ewes, mixtures of foliages from Jackfruit (Artocarpus heterophyllus) and cassava gave better ewe and lamb performance, when compared with mixtures of Jackfruit and Flemingia or Jackfruit alone.    

It is concluded that cassava foliage, which normally is left in the field as green manure, can be used as feed for small ruminants. In this way, farmers can get more benefit from their goats and sheep. Use of cassava leaves can also overcome the lack of grasses in the dry season, when most species of grasses are normally scarce. 

Key words: Growing goats, pregnant ewes, biomass yield, processing methods, nutritive value, intake, growth.

Introduction

Vietnam is a tropical country, with a total area about 33 million ha. The cultivated area is 11 million ha. The agriculture is mainly based on rice production with Cassava (Manihot esculenta) as a second crop after rice in the small-farm sector. The area of cassava cultivation in Vietnam is about 250,000 ha with a total production of 3,000,000 tonnes of roots per year. Cassava is normally planted in the hilly and mountainous area, where rice is difficult to grow. Most of the cassava root products are used for human consumption. However, some are used for animal feed and in the starch industry. 

In recent years, the Vietnamese government has paid more attention to small ruminant production. Therefore, the number of small ruminants has been increasing yearly and in 1997 there were 514,000 goats (FAO 1998). According to Dinh Van Binh et al (1995), 73% of the goat population is found in the north and the rest in the south. Most of the goats are concentrated in hilly or mountainous areas where integrated farming systems work well. Sheep are present in the Phan Rang area in Central Vietnam and Bavi district only. According to Nguyen Thi Mai and Nguyen Nhu Tan  (2001) the population of sheep in PhanRang area is 3,000 heads and in Bavi district around 200 heads.

Bavi district is located in a mountainous area in the west of Hatay province in North Vietnam. The district has an area of 421 km², consisting of 80% of sloping land. About 14,900 ha of the land is used for agriculture with around 10,000 ha of cassava production. There are about 8,000 ha of unused land, which can be used for pasture and forest. Nearly 2,000 goats are distributed in the hilly and mountainous area of Bavi district due to the potential of pasture and forest in this area. Small ruminant production is playing an important role in the improvement of incomes for poor farmers in hilly and mountainous areas of Bavi district, and is contributing to poverty and hunger alleviation in Vietnam. The potential of cassava in Bavi area is large, but utilization of cassava as small ruminant feed is not yet taken up by the farmers. This review will discuss the processing methods and the use of cassava as feed for small ruminants. 

Productivity of cassava

Cassava is a tropical shrubby perennial plant with a palmate leaf formation producing tubers at the base of the stem. Cassava thrives in sandy-loam soils with low organic matter, in areas receiving low rainfall and with high temperatures (Wanapat et al 1997). According to Nguyen Thi Mui et al (1994),  in North Vietnam the leaf biomass available when the root is harvested is about 5 tonnes per ha. The root biomass yield is of the order of 15 tonnes/ha (Table 1). An important point is that the harvesting time of cassava in North Vietnam coincides with the dry season, when air humidity is very low, convenient for sun-drying of the products. However, cassava is cultivated primarily for its roots and the foliage is generally left in the field as a green manure. Only small amounts of fresh cassava foliage, including the tender stem are used directly for animal feeding.  

 
Nutrient composition

The protein content of cassava leaves is relatively high for not being a leguminous plant (Table 2). Data reported in the literature show a range of from 20 to 40% of crude protein on dry matter basis. However, the crude protein content in the root is very low, around 4% in dry matter.  

Cassava root has a high content of carbohydrates (64-72 % of the total DM), with nearly 99% as amylose and amylopectin (Johnson and Raymond 1965). Cassava root is rapidly degraded by rumen micro-organisms. 

Processing

Sun-drying of roots and leaves is the method of processing commonly used by farmers. After harvesting, the roots are cleaned, chopped by hand or by machine into small pieces and sun-dried for about 3 days at  air temperature, around 32⁰ C. Then it is stored in plastic bags for human consumption or animal feed. Cassava leaves (including tender stems) are chopped into pieces of 1-2 cm and sun-dried until the dry matter is 90 %, before storing in plastic bags.

Another method for preserving fresh cassava root for animal feed is to ensile with salt. Cassava root is smashed into small pieces and ensiled with 2 kg salt per 100 kg fresh root in plastic bags, pits or tanks.

Feeding value of cassava for small ruminants

The low nutritive value of tropical grasses and roughage, and the lack of feed in the dry season are very common features which influence small ruminant production systems in Vietnam, especially in hilly and mountainous areas. Therefore, there is a need to find new feed resources to be used as low-cost supplements to improve animal productivity, especially in the dry season. In this context, protein-rich foliages such as Flemingia (Flemingia macrophylla), Jackfruit (Artocarpus heterophyllus) and Trichanthera gigantea are being promoted as protein supplements for livestock. Despite its availability and high protein content, there has been little interest until recently to utilize fresh cassava foliage for animal feeding. This reluctance is probably related to the fear of cyanide toxicity. However, work in Cambodia and Vietnam has shown that there is no risk of toxicity when fresh cassava foliage is fed to either goats (Seng Sokerya  and Rodriguez 2001);  or cattle (Ho Van Do et al 2001; Seng Mom et al 2001), provided the animals are adapted gradually to this feed..

Three combinations of dried foliages were formulated with different proportion of rice bran, cassava root meal and molasses (Table 3):

• MFC: 25% dried cassava leaves + 25% dried Flemingia foliage + 50% of each of five combinations of rice bran, cassava root meal and molasses
• MF:  50% dried Flemingia foliage +50% combination of rice bran, cassava root meal and molasses
• MC: 50% dried cassava leaves + 50% combination of rice bran, cassava root meal and molasses

Fresh para grass (Brachiaria decumbens) was also fed at the level of 20% of the diet dry matter.

The results in Table 4 show that the combination of 25% dried cassava foliage + 25% dried Flemingia foliage + 11% rice bran + 11% cassava root and 28% molasses gave the most positive effect on the performance of the goats. The data in Table 5 show the negative effect of including more than 20% (DM basis) of para grass in combination with the mixture of foliages. 

 
Effect of different foliages in the diet in late pregnancy on ewe and lamb performance

Cassava leaves and cassava root were used in the diets with local feed resources such as Jackfruit, Flemingia, sugar cane, rice bran and molasses-urea block (MUB) for pregnant ewes (Do Thi Thanh Van and Ledin  2001). The results are shown in Table 6. The DMI of dried cassava foliage was higher than DMI of Flemingia, when the same amount was offered in the diet. The combination of Jackfruit (JF) and cassava (CS) foliage in treatment JF+CS gave significantly higher feed intake (DM, CP, ME) than the diet with Jackfruit alone in JF treatment.  Jackfruit mixed with cassava tended to result in a higher feed intake than Jackfruit mixed with Flemingia (FM) in JF+FM treatment.

In the study of the effect of diet on body weight changes of the ewes and litter weight of lambs (Table 7), the highest weight gain during the last 8 weeks of pregnancy, and the heaviest litters at birth, were obtained from ewes fed with the mixed leaves of Jackfruit and cassava.

 
Conclusions

Cassava is considered to be an important crop in the hilly and mountainous areas of Bavi, which are not suitable for rice. Cassava root is mainly used for human consumption, but some is used as animal feed in dried or ensiled form. Cassava leaves, which normally are left in the field as green manure, can be used as feed for small ruminants. In this way, farmers can get more benefit from their goats and sheep. Use of cassava leaves can also overcome the lack of grasses in the dry season, when most species of grasses are normally scarce.     

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