Comparison of different forages as supplements to a basal diet of chopped cassava stems for growing goats

Trinh Xuan Thanh, Khuc Thi Hue, Nguyen Ngoc Anh and T R Preston*

Goat and Rabbit Research Center, Hanoi, Vietnam
Thanhgrrc@gmail.com
* TOSOLY, AA48, Socorro, Santander del Sur, Colombia

Abstract

Thirty two Bach Thao goats with an initial weight of 15.3 kg at 4 months of age were used to study the nutritive value of chopped cassava stems supplemented with Guinea grass or one of three protein-rich foliages - fresh cassava foliage (CF),  cassava hay (CH) or fresh jackfruit foliage (JF).

Highest values for total DM intake were recorded with supplements of fresh cassava foliage and jackfruit with the lowest value when the supplement was Guinea grass.  Growth rates were increased by 79%, and feed conversion improved by 34%, when the cassava foliage was fed fresh rather than being made into hay;  while compared with Guinea grass the growth on fresh cassava foliage as the supplement was 99% greater and the DM feed conversion 35% better. 

Key words: Bach Thao, cassava foliage, cassava hay, feed conversion, guinea grass, jackfruit foliage

Introduction

Cassava (Manihot esculenta Crantz) is one of the four most important crops in Vietnam, but it has always been a secondary crop after rice. In the last decades, especially since the late 1970s, cassava has played an important role in national food security. Recently, cassava has become an important source of cash income for farmers, who use it for animal feed and/ or for sale as substrate to starch factories (Kim et al 2008). Originally introduced from South America, it has expanded widely to Asia and Africa.  Cassava is now cultivated in 105 countries, mainly for root production as a source of energy and for foliage as a protein-rich supplement for animals. The amount of cassava foliage produced at root harvest is Vietnam is estimated at about 2.8 million tonnes yearly and there is a potential to increase this amount by harvesting more than once during the growth cycle (Hue et al 2010).

Cassava stems are not normally considered as forage and usually are separated from the leaves after root harvesting. Only a small amount of stems is used for planting in the next cultivation. Most are thrown away or used for fuel. According to Akinfala et al (2001, 2002), the tender stems can contain up to  11% crude protein in DM and could be included as part of the whole plant, to be used as feed for pigs and poultry. In traditional practice,  the farmers in the Bavi area close to GRRC, have been using cassava stems as the fibrous feed for goats, sheep and even dairy cattle in the dry season when roughages are in short supply. 

The objective of this study was to investigate the potential nutritive value for growing goats of fresh cassava stems when supplemented with available protein-rich foliages.

Materials and Methods

Location

The experiment was carried out at the Goat and Rabbit Research Center (GRRC), Sontay, Hanoi, Vietnam, longitude E 105°25 and latitude N 21°06. The altitude is about 220 m above sea level. The climate in this area is tropical monsoon, with a wet season between April and November and a dry season from December to March. Average annual rainfall is 1850 mm. The present trial was conducted from August to November 2011.

Experimental design

Thirty two growing goats were given a basal diet of chopped cassava stems plus a rumen supplement and one of of the following forages:

• GG: Guinea grass
• CH: Cassava hay
• CF: Fresh cassava foliage
• JF: Jackfruit  foliage

Each forage was offered at the rate of 1.5 kg DM  per 100 kg live weight. The cassava stems were fed ad libitum and the rumen supplement at 2 g/kg live weight. The length of the trial was 12 weeks.

Experimental feeds and animals

The foliages and Guinea grass were harvested in the fields of GRRC one to two hours before feeding. During rainy days, the forages were harvested the day before feeding to limit the effects of low DM content. The Guinea grass and cassava stems were chopped into pieces of 7-10 cm and 1-2 cm in length, respectively, before being offered to the goats in the feed trough. Cassava and jackfruit foliages were harvested at 50 to 60 cm above soil level and were offered by hanging in bunches in front of the feed troughs. The cassava variety used was K98-7 (medium bitter variety). The rumen supplement was:  (%) 10 urea, 20 molasses, 2 sulphur, 5 calcium phosphate, 5 salt and 58 rice bran.

The goats were of the Bach Thao breed (equal numbers of males and females) with an initial body weight from 15 to16 kg and about 4 months of age. Before starting the experiment, they were treated against parasites with injections of Ivermectin solution (1 ml per 4 kg LW) and vaccinated against pasteurellosis, enterotoxaemia, foot and mouth disease and goat pox. They were kept in separate cages, fed individually and were adapted to the experimental feeds for 10 days before starting the collection of data.  Cassava stems were fed at 7:30 and 14:30, while the foliages were given at 10:30 and 16:30. Mineral lick blocks (510 g limestone meal,  210 g bone meal plus 170 g cement as a binding agent and 100 g salt] were available ad libitum by hanging on the walls of the pens. Water was given freely for goats via water nipples. Feed offered and refused was recorded daily. The goats were weighed at weekly intervals.

Management

The animals were allowed to exercise once daily for one hour in the afternoon from 14.00 h to 15.00 h. During the exercise time, males and females were separated to avoid mating.

Measurements and chemical analysis

Samples of feed offered and refused were taken weekly for analysis of DM, then pooled as monthly samples for further analysis of crude protein (CP), neutral detergent fiber (NDF), acid detergent fiber (ADF) and ash. Dry matter and ash were analysed according to the standard methods of AOAC (1990). Nitrogen was determined by the Kjeldahl procedure. NDF and ADF were determined by the methods of van Soest et al (1991).  

Statistic analysis

The data were analysed statistically using the GLM option of the ANOVA program in the Minitab Software (Minitab 2008). The statistical model used in the analysis of the growth trial was:

Y_ijk = m + T_i + e_ijk, where Y_ijk  is the dependent variable, m the overall mean, T_i the effect of treatment (diets), and e_ijk the random error, independent and normally distributed. Treatment means which showed significant differences at the probability level of P<0.05 were compared using Tukey’s pairwise comparison procedure in the Minitab (2008) software.

Results and discussion

The CP and the ash values in the cassava stems were very low (Table 1); however they had lower concentrations of both NDF and ADF than the Guinea grass.

Highest values for total DM intake were recorded with supplements of fresh cassava foliage and jackfruit with the lowest value when the supplement was Guinea grass (Table 2). The daily intake of cassava stems as the basal feed was not affected by the source of the supplement; however, because of lower intake of the Guinea grass supplement, the proportion of the diet DM represented by the cassava stems was 78% on this diet compared with a range of 43 to 56% for the supplements of  cassava hay, cassava foliage and jackfruit.

Growth rates were increased by 79%, and feed conversion improved by 34%, when the cassava foliage was fed fresh rather than being made into hay (Table 3; Figures 1 and 2);  while compared with Guinea grass the growth on fresh cassava foliage as the supplement was 99% greater and the DM feed conversion 35% better. Similar advantages from feeding fresh rather than sun-dried cassava foliage were reported for goats by Kounnavongsa et al (2010). Another advantage from feeding fresh rather sun-dried cassava foliage appears to be the reduced methane production recorded in an in vitro rumen fermentation study by Le Thi Binh Phuong et al (2012).

Figure 1. Growth rates of goats fed a basal diet of chopped cassava stems, supplemented with different foliages	Figure 2. DM feed conversion of goats fed a basal diet of chopped cassava stems, supplemented with different foliages

Conclusions

• Cassava stems can be used effectively as the basal carbohydrate feed for goats provided they are supplemented with a protein source known to provide bypass protein.

• Fresh cassava foliage supports better growth and feed conversion than cassava hay when used as the protein source for a low-protein basal diet such as cassava stems

References

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Akinfala E O, Aderibigbe A O and Matanmi O 2002 Evaluation of the nutritive value of whole cassava plant as replacement for maize in the starter diets for broiler chicken. Livestock Research for Rural Development. Volume 14, Article #56. http://www.lrrd.org/lrrd14/6/akin146.htm.

AOAC 1990 Association of Analytical Chemists, 15th ed. Official Methods of Analysis, Washington, DC.

Kim H, Ngai N V, Howeler R and Ceballos H 2008 Current situation of cassava in  Vietnam and its potential as a bio-fuel. http://cassavaviet.blogspot.com/2008_09_01archive.html.  

Hue K T, Van D T T, Ledin I, Sporndly E and Wredle E 2010 Effect of feeding fresh, wilted and sun-dried foliage from cassava (Manihot esculenta Crantz) on the performance of goats and their intake of hydrogen cyanide. Livestock Science  131 (2), 155-161. http://pub.epsilon.slu.se/8617/1/Hue_k_t_120306.pdf

Le Thi Binh Phuong, Preston T R and Leng R A 2012 Effect of foliage from “sweet” and “bitter” cassava varieties on methane production in in vitro incubation with molasses supplemented with potassium nitrate or urea. Livestock Research for Rural Development. Volume 24, Article #189. http://www.lrrd.org/lrrd24/10/phuo24189.htm

Kounnavongsa B, Phengvichith V and Preston T R 2010 Effects of fresh or sun-dried cassava foliage on growth performance of goats fed basal diets of Gamba grass or sugar cane stalk. Livestock Research for Rural Development. Volume 22, Article #202. http://www.lrrd.org/lrrd22/11/boun22202.htm

Minitab 2008 Minitab user's guide. Data analysis and quality tools. Release 18.1 for windows. Minitab Inc., Pennsylvania, USA.

van Soest P J, Robertson J B and Lewis B A 1991 Methods for dietary fiber, neutral detergent fiber and non-starch polysaccharides in relation to animal nutrition. Journal Dairy Science 74, 3583-3597.

Received 9 June 2012; Accepted 14 December 2012; Published 4 January 2013

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