Livestock Research for Rural Development 14 (3) 2002

http://www.cipav.org.co/lrrd/lrrd14/3/do143b.htm

Effect of supplementation of ammoniated rice straw with cassava leaves or grass on intake, digestibility and N retention by goats

Ho Quang Do, Vo Van Son, Bui Phan Thu Hang, Vuong Chan Tri and T R Preston*

College of Agriculture, Cantho University, Cantho, Vietnam
hqdo@ctu.edu.vn
* University of Tropical Agriculture Foundation, Phnom Penh, Cambodia
regpreston@utafoundation.org

Abstract

Five goats (Bach thao breed) of 11.7 ± 6.4 kg live weight receiving a basal diet of ad libitum ammoniated rice straw (4% urea treatment) were allocated to a 5*5 Latin Square arrangement to compare forage supplements (10 kg/100 kg live weight, fresh basis) of: G, fresh grass; GC1, fresh grass and fresh cassava leaves (75:25 DM basis); GC2, grass and cassava leaves (50:50 DM basis); GC3, grass and cassava leaves (25:75 DM basis); and C, fresh  cassava leaves. 

Increasing the intake of cassava leaves over the range 0 to 47% of the diet DM led to related increases in all measured parameters: intake of ammoniated rice straw, total organic matter and total dry matter; digestibility of organic matter, N, crude fibre and ash; and  daily retention of N.

Key words: Ammoniated rice straw, cassava leaves, digestibility, goats, intake, nitrogen retention

Introduction

Fermentable N, bypass protein and minerals are the major  factors limiting ruminant performance on cereal straws (Preston and Leng 1987). Thus the combination of supplementary cottonseed meal (rich in bypass protein) and ammoniation of the straw (to increase digestibility and content of fermentable N) have resulted in tripling of the growth rate of cattle to levels of almost 1 kg/day (Zhang Weixian et al 1994).

In Vietnam, goats are raised by the poorest farmers who live in the most abandoned areas. The farmers consider the advantage of these animals to be their capacity to grow and reproduce on locally available feed resources. In order to develop an economical way of fattening goats on straw in Vietnam, it will be necessary to find sources of protein which can be made available locally, preferably being grown by the farmer who will fatten the goats.    

Cassava is widely grown in Vietnam and the leaves are a potential source of protein available at farm level. Ffoulkes and Preston (1978) showed that fresh cassava foliage as the sole source of fibre and protein in a diet of liquid molasses and urea (3% urea) supported growth rates of almost 900 g/day and there was no advantage in providing additional soyabean meal. Supplementation with fresh cassava leaves improved the consumption and performance of cattle fed a basal diet of untreated rice straw (Ho Van Do et al 2002; Seng Mom et al 2001) and of goats fed a basal diet of spent brewer’s grains (Seng Sokerya and Rodríguez 2001). Dried cassava leaves  (cassava hay) were effective in increasing the growth rate of cattle fed ammoniated straw (Wanapat et al 1992).while cassava leaf meal supported the same performance as cottonseed meal when used as a supplement for lactating goats (Duong Thanh Liem et al 2000).  

The study reported in this paper aimed to compare the relative effects of supplements of different proportions of fresh grass and fresh cassava leaves on intake, digestibility and N retention in young goats fed ammoniated (with urea) rice straw.
 

Material and methods

Location, treatments and design

The trial was carried out on the experimental farm of the Department of Animal Husbandry of Cantho University. Five Goats (Bach thao Breed) of 11.8±6.4 kg live weight receiving a basal diet of ad libitum ammoniated rice straw were allocated to five supplements (10 kg/100 kg live weight, fresh basis) of:

• G, fresh grass;

• GC1, fresh grass and fresh cassava leaves (75:25 DM basis);

• GC2, grass and cassava leaves (50:50 DM basis);

• GC3, grass and cassava leaves (25:75 DM basis);

• GC, fresh  cassava leaves.

The experimental design (Table 1) was a 5*5 Latin square arrangement. Each period was of  20 days, 15 days for adaptation and five days for measurement of digestibility and N retention.

Feeding system

Dry rice straw was purchased from local farmers and treated with urea (4 kg urea, 100 kg straw, 50 kg water) and stored in sealed polyethylene bags. Plantations of grasses (Brachiaria mutica (forsk) Stapf) were available at the University farm.  The growing of the cassava forage was done in cooperation with a local farmer. The need for the total experiment was calculated as 5 animals * 1 kg/day * 56 days = 280 kg. This required an area of 560 m².as average yields are 0.5 kg/m² of fresh leaves and the cassava can be harvested at intervals of 56 days. Only leaves and petioles were fed.

The urea-treated rice straw was offered ad libitum, fresh quantities being given morning and afternoon  to ensure there was a residue of rice straw of at least 0.5 kg. The grass and cassava leaves (mixed where necessary) were given fresh in a single feed in the morning at a level of 10 kg for each 100 kg live weight.

Feed analysis

During the collection period, samples of rice straw were taken once per week, while samples of cassava leaves were taken every day and pooled weekly. DM content was determined on pooled samples. Feed refusals were collected from individual animals and weighed every day. Samples of faeces and urine were collected every morning, weighed and kept in the deep freezer. N H₂SO₄ was added to the urine bucket in quantities sufficient to maintain the pH below 4.0.

The feeds and refusals in the digestibility study were analyzed for DM, ash, organic matter (OM), Nitrogen (N) and crude fiber (CF), according to AOAC (1990).  

Statistical analysis

The data from the experiment were statistically analysed by ANOVA using the General Linear Model (GLM) of Minitab Software (versopn 13.2). Variables were treatments, periods, animals and error.
 

Results and discussion

Diet composition

Ammoniation of the rice straw by ensiling with urea increased the crude protein content to 9.6% in dry matter (Table 2), which is in line with data in the literature (see review by Chemost and Kayouli 1997). The level of crude protein in the cassava leaves (23.6%) was within the range reported by many authors (see Ly and Rodríguez 2001).  The grass was cut at an early vegetative stage (10% DM) which explains the relatively high crude protein content. Crude fibre in the cassava leaves was slightly less than half that in the grass and the ammoniated straw. 

All the grass and cassava that were offered were consumed. However, in the case of the mixtures, it was noted that the goats first ate the cassava leaves  before consuming the grass. Increasing the proportion of cassava leaves in the diet had marked positive effects on all the measured  parameters (Tables 3).  Intake of urea-treated rice straw was increased by more than 100%, while total intake of  DM was increased by . 38%, at the highest level of cassava foliage. There was  a curvilinear increase in daily N retention as the proportion of cassava leaves in the diet was increased (Figure 1).
 

 

 

Figure 1:  Effect of proportion of cassava leaves in the diet on N retention

The results of this experiment support the increasing number of reports demonstrating the important role played by the cassava plant as a source of protein as well as carbohydrate for ruminant animals (see reviews: Preston 2001; Wanapat 2001). The need to return to the soil the nutrients extracted by repeated harvesting of the foliage is now well understood (Preston 2001), thus permitting the diversified use of this high yielding crop as a component of integrated farm systems.
 

Conclusions

Increasing the intake of cassava leaves over the range 0 to 47% of the DM, of a basal diet of ammoniated rice straw, led to significant increases in:

• Intake of ammoniated rice straw, total organic matter and total dry matter;

• Digestibility of organic matter, crude fibre and ash;

• Daily retention of N.

References

AOAC 1990 Official methods of analysis, Association of Official. Analytical chemists. Washington, DC  

Chenost M and Kayouli C 1997 Roughage utilization in warm climates. FAO Animal Production and Health Paper 135. FAO: Rome