Effects of fresh or sun-dried cassava foliage on growth performance of goats fed basal diets of Gamba grass or sugar cane stalk

Bounthavone Kounnavongsa, Vanthong Phengvichith* and T R Preston**

Livestock Research Center, National Agriculture and Forestry Research Institute
kounnavongsa@gmail.com   ;   kounnavongsa@yahoo.com
* National Agriculture and Forestry Research Institute. Ministry of Agriculture and Forestry, P.O. Box 811, Vientiane Laos
** Finca Ecológica, UTA-Colombia, AA#48, Socorro, Santander, Colombia

Abstract

 A trial to measure the  growth performance of young goats (Capra spp.) was carried out during a 3 month period at the experimental farm of Livestock Research Center, Vientiane, Laos to study the effect of feeding fresh cassava foliage or sun-dried cassava foliage in diets based on based on Gamba grass or sugar cane stalk. Twenty four goats of which twelve males and twelve females with the average body weight of 10.3 kg and at the age of 6 to 7 month old were randomly allocated to four treatments of six animals according to weight and sex. The experimental feeds were Gamba grass (Andropogon gayanus cv. Kent) and sugar cane stalk (Saccharum officinarum) as basal diets, supplemented with fresh cassava foliage or sun-dried cassava foliage (Manihot esculenta, Crantz). Feeds were offered ad libitum.

DM intake and daily weight gain were higher, and feed conversion better,  for goats fed fresh cassava foliage than for those fed sun-dried cassava foliage. There were no differences between Gamba grass and sugar cane in weight gain but feed intake was higher and feed conversion poorer on the Gamba grrass.  The cassava foliage was a higher proportion of the total DM intake on the sugar cane diet (53%)  than on the Gamba grass diet (32%) and on dry (50%) than on fresh cassava foliage. There were no symptoms of HCN toxicity in the goats fed the fresh cassava foliage.

In conclusion, the daily weight gain was highest when using Gamba grass as basal diet supplemented with fresh cassava foliage and the better DM feed conversion was  for the treatment using sugar cane supplemented with fresh cassava foliage.

Key words: growth, local goats.

Introduction

Livestock are an important component of smallholder farming systems in Laos with sales which account for more than 50% of the family cash income. Livestock provide great benefits to farmers such as high nutritive value food, generating income and manure which is very important for maintaining soil fertility. They also provide draught power for transportation and crop production. They serve as financial assets so livestock offer an alternative for storing their savings or accumulated capital as a "living savings account". Keeping livestock is considered as an alternative form of insurance; they also enhance family status because the value of livestock can be an indicator of social importance. Over 95% of all livestock is produced by smallholders. The goat population in Laos is estimated to be about 268,900 heads (DLF 2007). It is relatively small compared to neighboring countries in the region. However, the population is increasing, with an annual growth rate of 8%. Most goats are native breeds, with small body size and low growth rates. Goats are generally allowed to graze freely all year round in small groups in the forest, fallow cropland and roadside. According to Phengsavanh and Ledin (2003) a major constraint to livestock production in Lao PDR is feed shortage in both quality and quantity, and especially the protein sources. The main feed resources are native grasses, shrubs, legumes and tree leaves that are available in forests, grasslands, fallow land and agricultural by-products. Parasitism is the main problem under low level management conditions with the mortality rate up to 50%. Goats are also less resistant to intestinal parasites compared to other ruminants.

The great challenge is to make the goats become environmentally friendly through the changing of the free range farming system to stall feeding system. Farmers tend to restrict their herds in order to avoid excessive damage to crops, for which the owner is held responsible. In recent years (Phengsavanh and Ledin 2003), goat management practices have been changing, and vary from site to site depending mostly on land availability, labor and community regulations. Goats are reared only for meat and they reach a mature weight of about 40 kg in 2-3 years under local conditions. First kidding is at 12-18 months of age, usually a single kid at the first litter and twin kids later.

Goats are browsers and highly selective, and they can withstand the harsh conditions such as seasonal shortages of feed which means they are well adapted to the local environment. According to their small body size, they need low capital investment, and need smaller areas to graze than cattle. Local goat breeds have high reproductive rate with a great genetic variability. However, little attention has been given to feeding, management and health so small inputs will probably give good results.

The great potential in the development of goat production in Laos is the high market demand for goat meat for local consumption and export. This is an incentive to intensify goat production as improved nutrition will lead to faster growth rates which will result in carcasses with higher content of meat.

Improved nutrition requires increasing the energy density of the diet, ensuring efficient rumen function and providing a complimentary source of bypass protein (Preston and Leng 2009).   Sugar cane contains a high content of soluble sugars and has been used successfully as the basis of an intensive system of fattening cattle (Preston et al 1976). The foliage of cassava (Manihot esculenta, Crantz) has been shown to be an effective source of bypass protein for fattening steers (Ffoulkes and Preston 1978; Wanapat et al 1997; Keo Sath et al 2008) and lactating dairy cows (Wanapat 2001). There is some controversy as to the potential toxic effects of the hydrocyanogenic glucosides present in fresh cassava foliage and which can give rise to liberation of HCN (Wanapat et al 1997). For this reason, sun-drying of the foliage has been recommended. On the contrary there are several reports (Ffoulkes and Preston 1978; Seng Sokerya and Rodriguez 2001; Theng Kouch et al 2003; Seng Mom et al 2001) in which cassava foliage was fed in the fresh state and where there were no indications of toxicity. There appear to be no reports in the literature of toxicity resulting from the feeding of fresh cassava to ruminants. There are also no reports where fresh and sun-dried cassava foliage has been compared in the same experiment.

Objectives

• The aims of the present research are therefore to investigate the potential to intensify goat production by feeding sugar cane as the basal diet.

Materials and methods

Location and climate

The experiment was carried out at the Livestock Research Centre, National Agriculture and Forestry Research Institute, which is located about 40 km North of Vientiane Capital, Laos at an altitude of 150 m above sea level. The experiment was conducted during the months of October to December 2009. The climate is tropical monsoon, with a dry season from November to April (only about 1 to 2% of the annual rainfall occurs during this season) and a wet season from May to October. The average annual precipitation is about 1765 mm, ranging from 1500 mm to more than 2000 mm. The highest rainfall occurs in June to August. The maximum temperature ranges from 35^oC to 42^oC in March to May and the minimum temperature from 18^oC to 22^oC in December to February. The soils are generally sandy loams with low fertility and an average pH of 4.5.

Treatments and experimental design

The nutritional treatments applied to 24 growing goats were:

• GBFC =  Gamba grass with fresh cassava foliage
• GBDC =  Gamba grass with sun-dried cassava foliage
• SCFC  =  Sugar cane stalk with fresh cassava foliage
• SCDC  =  Sugar cane stalk with sun-dried cassava foliage

The treatments were arranged as a 2*2 factorial in a randomized complete block design (RCBD) with six replications.  The animals were allocated to 6 blocks (Table 1) on the basis of sex (12 males and 12 females) and live weight.

Animals and management

Twenty-four local growing goats (Capra spp.) including 12 females and 12 males (non-castrated) weighing from 7.6 to 13.5 kg and about 6 to 7 months of age were housed in individual pens with raised slatted floors (Photo 5). The goats were bought from Savannakhet province in the Central part of Laos, 500 km from Vientiane.  They were treated against internal and external parasites with Ivomectin (1 ml/33 kg live weight), and then adapted to the pens and the trial feeds for 14 days before starting the experiment. The feeds were offered twice per day at 07:00h and 16:00h. The experiment lasted for 84 days excluding adaptation and organizing period.

Photo 1: sugar cane stalk chopped	Photo 2: Gamba grass
Photo 3: Fresh cassava foliage	Photo 4: Partially sun-dried cassava foliage
Photo 5: Experimental pens

Experimental feeds

Gamba grass (Andropogon gayanus cv. Kent) and sugar cane stalk (Saccharum officinarum) were used as basal diets and fed ad libitum. They were supplemented with cassava foliage (Manihot esculenta, Crantz) offered ad libitum in the fresh state or after partial drying in the sun and, during periods of rain, under shade. Gamba grass was collected from an existing forage area in the Livestock Research Center. The forage area was divided into 6 plots, each providing enough feed for 7 days, which were harvested in a 40 to 45 day rotation. It was manually harvested twice per day in the morning and afternoon. After each cutting, urea was applied in amounts of 80 kg /ha. Sugar cane stalk was purchased from farmers nearby the center every 2 to 3 days. It was chopped into 2 to 3 cm lengths using a small hand-operated cutting machine. Cassava was grown in the Livestock Research Center, but there was not always enough so the rest was purchased from farmers. It was collected daily, morning and afternoon. The foliages, dry and fresh, were hung as whole branches above the feed trough. Mineral blocks and fresh water were offered ad libitum separately in each cage during the whole experiment period.

Measurements

Samples of each feed offered and refused were taken every two weeks to determine DM by micro-wave radiation (Undersander et al 1993). The dried samples were pooled over two weeks and stored for later analysis. The amounts of each feed offered and refused were recorded daily for individual animals. Live weights were recorded every 14 days. The dried feed samples were analysed for crude protein (CP) and ash according to standard methods (AOAC 1980). CP was analyzed by the Kjeldahl method and was calculated as Nx6.25. Ash was calculated after incineration in a muffle furnace at 550^oC for 3 hours.

Statistical analysis

Data were analyzed using the GLM option in the ANOVA program of the Minitab 2000 software Version 13.1 (Minitab 2000). Sources of variation in the model were: forage, processing, interaction forage* processing and error.
 

Results

Chemical composition of the dietary components

The Gamba grass had higher levels of CP and ash than the sugar cane stalk (Table 2).

Feed intake, growth rate and feed conversion

The daily live weight gain did not differ between sugar cane and Gamba grass but was higher for fresh than sun-dried cassava foliage (Tables 3 and 4 and Figures1 and 2). By contrast, the DM feed intakes were lower for fresh versus dried cassava foliage (Figure 3) and for sugar cange (Figure 3) and for sugar cas broad dietary e versus Gamba grass (Figure 4). As a result, the feed conversion was better for fresh than for dried cassava foliage (Figure 5), and for sugarcane rather than Gamba grass (Figure 6).

Figure 1: Contrasting effect of cassava foliage (dried or fresh) on growth rate of goats fed basal diets of Gamba grass and sugar cane	Figure 2: Contrasting effect of Gamba grass versus sugar cane on growth rate of goats fed dried or fresh cassava foliage
Figure 3: Contrasting effect of cassava foliage (dried or fresh) on feed intake of goats fed basal diets of Gamba grass and sugar cane	Figure 4: Contrasting effect of Gamba grass versus sugar cane on feed intake of goats fed dried or fresh cassava foliage
Figure 5: Contrasting effect of cassava foliage (dried or fresh) on feed conversion of goats fed basal diets of Gamba grass and sugar cane	Figure 6: Contrasting effect of Gamba grass versus sugar cane on feed conversion of goats fed dried or fresh cassava foliage

Discussion

As far as the authors are aware the present study is the first to compare feeding goats with fresh and sun-dried cassava foliage derived from the same stand of cassava.  The results showed clearly that the fresh foliage supported superior growth and feed conversion to the dried form, on both basal diets of Gamba grass and sugar cane. Moreover, the levels were very high reaching to 62% of the total DM intake when the dried cassava foliage was fed together with the sugar cane. The proportion of the diet as cassava foliage was higher on sugar cane than on Gamba grass and higher for dried versus fresh foliage. These contrasting results between the fresh and “partially” dried cassava foliage are difficult to explain.  Total DM intakes were higher when Gamba grass was the basal diet.  It may be that the goats found the “young” Gamba grass more palatable than the “mature” sugar cane and therefore compensated by eating more cassava foliage when sugar cane was the basal diet. The relatively large size of the pieces of chopped sugar cane may also have been a deterring factor. The chopping machine had been designed to process fresh forages and did not perform adequately on the “tough” outer rind of the sugar cane, resulting in pieces of stalk of 2 to 3cm thickness.  Practical experience in Mexico (Preston et al 1976) with cattle and with goats in Colombia (Lylian Rodriguez 2009, personal communication) indicated that fine grinding using a “high-speed” silage chopper resulted in higher intakes of sugar cane.

There is a wide range of recent literature showing the beneficial effects of cassava foliage on growth rates and feed conversion of cattle (Ho Thanh Tham et al 2008, Keo Sath et al 2008, Seng Mom et  2001), goats (Seng Sokerya and Rodriguez 2001, Ho Quang Do et al 2002, Ho Bunyeth and Preston 2004) and on milk yield in dairy cattle (Wanapat 2001). In these different experiments, the cassava foliage was prepared and fed in many different forms: fresh, wilted or ensiled. Wanapat et al (1997) recommended the drying of cassava foliage “not only to reduce moisture but also to decrease hydrocyanic acid to a safe level for ruminants”.  However, the implication that the precursors of hydrocyanic acid (HCN) are a constraint to the feeding of cassava foliage to ruminants has not been tested in the same experiment.  Ffoulkes and Preston (1978) fed fresh cassava foliage as the sole source of roughage and protein in a diet of liquid molasses-urea) and reported growth rates of over 700 g/day in young cattle, similar to what was achieved with soybean meal.  No health problems were observed that could have been caused by the presence of HCN precursors.

The presence of cyanogenic glucosides in cassava foliage is often considered to to be a "risk" factor, as hydrogen cyanide (HCN) is released when the intracellular glucoside becomes exposed to the extracellular enzyme linamarase (Tewe 1992).  Methanogens are highly sensitive to HCNhydrogen cyanide (Cuzin and Labat 1992 ) thus the presence of higher levels of cyanogenic glucosides in fresh cassava foliage, as compared with sun-dried foliage, may have had the indirect effect of reducing methane production. This in turn would a higher concentration of useful metabolites in the rumen fermentation and potentially higher growth rates. Further support for this idea can be found in a recent report showing a lower methane:carbon dioxide ratio in goats fed sugar cane and fresh cassava foliage compared with goats fed Guinea grass and concntrates (Nguyen Ngoc Anh et al 2010).

Conclusions

• Fresh cassava foliage resulted in 35% higher weight gain and 36% better feed conversion compared with the sun-dried form.

Acknowledgements

The authors gratefully acknowledge the Swedish International Development Agency (Sida) for the financial support of this study. We are also grateful to all staff members of Livestock Research Centre for valuable help during the field operation.
 

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