Comparison of water extractable dry matter and neutral detergent fibre as indicators of whole tract digestibility in goats fed diets of different nutritive value (Guinea grass, Cassava foliage, Stylosanthes, Water spinach)

Pheng Buntha

Center for Livestock and Agriculture Development
(CelAgrid, UTA-Cambodia)
Phnom Penh, Cambodia
tha_vt@yahoo.com

Introduction

The use of foliage from trees and shrubs in animal nutrition has focused the attention of many researchers, due to the fact that these feed resources are locally available, perennial sources of feeds (Singh 1995; Leng 1997), rich in protein and particularly appropriate for small ruminants (Seng Sokerya and Rodriguez 2001).

Nowadays many researchers are interested with the method for studying the digestibility of diets such as in vivo, in sacco, and in vitro, and also the use of indicators of digestibility such as crude fibre and NDF. Nguyen Van Thu (2005) reported that the supplement of sesbania leaves to rice straw fed on buffaloes significantly improved in vivo DM and NDF digestibility but had no effect on in vitro measurements of digestibility nor on parameters in the in sacco test. Furthermore, Ly and Preston (1997) suggested that washing losses of dry matter (WL) could be a very simple parameter to assess the overall process of leaf degradation in the rumen ecosystem. Ly et al (1997) concluded that the washing loss test has good potential as predictor of in vitro gas production in the rumen ecosystem. On the other hand, the washing loss was closely related with in sacco digestibility, ranking the species similarly; and was considered to be equally effective in rating the chosen materials as potential sources of digestible dry matter for both ruminant and monogastric livestock. It was recommended that the use of the washing loss method could be a first approximation to estimation of nutritive value as it is simple, rapid, and low cost, and dispenses with the need for surgically modified animals (Ngugen Van Lai and Nguyen Thi Thu Huong 1999).

Cassava foliage (Manihot esculenta) is mainly available as a crop residue after harvesting the roots. Nevertheless, it has been claimed that cassava cultivation for forage purposes could be an advantageous alternative in integrated farming systems (Preston 2001). Moreover, Theng Kouch et al (2003b) showed that goats adapt readily to consumption of fresh cassava leaves. Seng Sokerya et al (2003) also reported that the feeding of cassava foliage rather than grass can reduce nematode infestation and give a good growth rate in the goats. DM digestibility was 68.8 and 73.1 for goats fed leaves and foliages in the feed trough, and about 80.1% to 83.5% of DM when the foliage was suspended from the roof as well as better feed intake as the sole diet to growing goats (Him Aun 2002; Theng Kouch et al 2003b).

Stylosanthes guinensis CIAT 184 (Stylo 184) is a short-lived perennial legume (2 to 3 years) that grows into a small shrub with some woody stems. It is usually grown as a cover crop, which is cut every 2 to 3 months (Horne and Stür 1999). N concentrations of Stylosanthes guianensis range from 1.5 to 3 % in DM. DM digestibility of young plant material lies between 60 to 70%, but with increasing age and lignification this may be reduced to below 40% (Mannetje and Jones 1992). Furthermore, Phonepaseuth Phengsavanh and Inger Ledin (2003) reported that increasing the amount of Stylo 184 in the diet of goats  resulted in increasing intake of total DM, CP, NDF and ADF. The highest total DM intake, approaching 3% of body weight, was obtained in the diets with 30 and 40% Stylo 184. The highest daily weight gain was 70 g/day with 40% Stylo 184, but was not significantly different from the diet with 30% of Stylo 184 (64 g/day).

Guinea grass (Panicum maximum) is the most productive forage grass in tropical America, valuable for pasture, green-soilage, hay, and silage. Especially palatable in the younger stages, it tends to become coarser and less readily eaten by cattle as it matures. However, because of its lack of good seed production, its use is limited (Reed 1976). Per 100 g, the forage is reported to contain (DM basis): 5.9 g protein, 1.6 g fat, 81.9 g total carbohydrate, 35.7 g fiber, 10.6 g ash, 2090 mg Ca, and 590 mg P (Duke and Atchley 1984).

Water spinach (Ipomea aquatica) has high biomass yield and high nutritive value for rabbits (Honthong Phimmasan et al 2004) and pigs (Chhay Ty and Preston 2005). There appears to be no information on its feeding value for goats.

Hypothesis:

Water extractable  DM of a feed is a better indicator of in vivo digestibility than NDF (neutral detergent fibre).

Objectives:

To compare the nutrient digestibility of Guinea grass, fresh cassava foliage, stylosanthes grass, and water spinach in goats and to determine the relationship between water extractable DM and in vivo digestibility compared with the relationship between NDF and in vivo digestibility.

Materials and Methods

Location

The study will be carried out at the Livestock Research Center, in Laos, from September to October, 2005.

Treatments and design

Foliage of guinea grass, fresh cassava (Manihot esculenta), stylosanthes and water spinach will be used.  All these foliages will be from plantations in LRC and will be harvested periodically.

Four foliages will be compared in a completely randomized block design with 3 goats (blocks) and 4 periods (see Table 1), with 8 days in each period, 3 days for adaptation and another 5 days for data collection..

Feed intake, nutrient digestibility, and N retention will be determined.

Animals and housing

Two female goats and one male goat averaging 11 kg live body weight will be used for the evaluation of every plant species. The goats will be housed in metabolism cages (1.0x0.8 m), elevated 0.7 m and allowing the separate collection of faeces and urine. The cages will made of wood and will be situated in a shaded building with roof and open sides .

Feeding management

The feeds will be offered ad libitum.   The guinea grass, fresh cassava foliage, stylosanthes foliage and water spinach will be offered fresh as the sole feeds, immediately after harvesting. The feed will be offered as the whole branch and will be suspended from the roof of the cage.  The goats will be offered the feed three times per day (7:00 AM, 12:00 AM and 4:00 PM).

Measurements

Feed offered and refused, output of faeces and urine, will be recorded daily during the last 5 days of each period. Samples of feed offered and refusals will be taken daily and analysed for DM , N, and NDF. 10% of faeces will be put each day in plastic bags in the freezer (-20 °C). Urine will be collected in a bucket containing 10 ml of 25% sulphuric acid (H₂SO₄) to keep the pH below 4 so as to prevent escape of ammonia. 10% will be collected each day and kept in the freezer. 

Chemical analysis

In the laboratory,  the wash value method (WL) (Ly and Preston 1997; Ly and Preston  2001) will be used to analyze the 4 different species of foliage. Tea bags will be used in duplicate to estimate the WL in a semi-automatic washing machine  About 1g (dry) of sample will be introduced in the bags and thereafter will washed for three consecutive cycles of 30 min each. The temperature and pH of the tap water utilized will be on average 25^oC and 6.6 respectively. The volume of water used in every cycle will be in the ratio of 3 litres per bag. After washing, the DM content in the residue in the bags will be estimated by microwave radiation to constant weight as described by Undersander et al (1993).

Feed and faecal samples will be dried by microwave radiation to measure the DM content (Undersander et al 1993). Total N of feed, faeces and urine will be measured by the Kjeldahl procedure as outlined by AOAC (1990). The ash content of feed and faeces will be determined following the AOAC (1990) recommendations and therefore, the organic matter will be assumed to be the result of subtracting the percentage of ash from 100. The NDF will be determined according to the method of Van Soest et al (1991).

Statistical analysis:

The data will be analyzed according to the analysis of variance technique  using the general linear model (GLM) procedure in the software of MINITAB (release 13.31). Relationships between wash value (independent variable) and digestibility (dependent variable), and NDF and digestibility,  will be determined using the regression models in the Excel software.

Work Plan

Table2. Work plan for doing experiment
Date	Activity for experiment
12 Sep- 15 Sep, 2005	Prepare the pen and adapt the goat with pen and feed.
15 Sep -23 Sep, 2005	Period 1 (3 day for adaptation and 5 days for collecting data)
23 Sep- 01 Oct, 2005	Period 2 (3 day for adaptation and 5 days for collecting data)
01 Oct- 09 Oct, 2005	Period 3 (3 day for adaptation and 5 days for collecting data)
09 Oct- 17 Oct, 2005	Period 4 (3 day for adaptation and 5 days for collecting data)
17 Oct – 23 Oct, 2005	Prepare the data analysis and write the paper and present the result

 

References

AOAC 1990 Official Methods of Analysis. Association of Official Analytical Chemists. 15th edition (K Helrick, editor). Arlington pp 1230

Duke J A and Atchley A A 1984 Proximate analysis. In: Christie B R (ed), the lant science in agriculture. CRC Press, Inc Boca Raton, FL.

FAO 1995 Regional Office for Asia and the Pacific Publication 1995/16. Bangkok pp 65

Him Aun 2002 A study of integration of goat production in a rubber tree plantation inCambodia. MSc. Thesis. University of Tropical Agriculture. Cambodia.

Leng R A 1997 Tree foliage in ruminant nutrition. FAO Animal Production and Health. Paper No 139. Rome pp 100