Comparison of cassava hay yield and chemical composition of local and introduced varieties and effects of levels of cassava hay supplementation in native beef cattle fed on rice straw

Phanthavong Vongsamphanh and Metha Wanapat^*

Livestock Research Center, National Agriculture and Forestry Research Institute,
Ministry of Agriculture and Forestry, Vientiane, Lao PDR
phanthavongkv@hotmail.com
^*Department of Animal Science, Faculty of Agriculture
Khon Kaen University, Khon Kaen 40002,Thailand
metha@kku.ac.th

Abstract

In the first experiment, a local and an introduced cassava variety (Rayong72; RY72) from Thailand) were studied to determine the effects on yields and chemical composition during three harvests (at 3, 5 and 7 months after planting).

Dry matter (DM) and protein yields of cassava variety RY72 at each harvest were higher than the local variety. Condensed tannin  was 3.3 to 3.4 and 3.5 to 3.8 %, in RY72 and local variety, respectively.

In the second experiment, the effect of level of cassava hay supplementation on rumen parameters, digestibility and rice straw intake in growing native cattle was studied. Four, 2-year-old rumen fistulated bulls were randomly assigned to a 4 x 4 Latin square design to receive four dietary treatments: 0, 200, 400 or 600 g/day of cassava hay during periods of 28 days.  The basal diet was ad libitum rice straw and 200 g/day of a rumen supplement  (5% urea; 95% rice bran ).Each feeding period consisted of 7 days adaptation, 14 days for rice straw intake measurement and was followed by a 7 days collection period of feed, rumen fluid, blood and fecal samples.  

Ruminal NH₃-N and blood urea nitrogen were not affected by level of cassava hay in the diet.  Bacterial and fungal zoospore populations were  increased while protozoal population was decreased as a result of  cassava hay supplementation. Digestion coefficients particularly those of DM, OM, and CP were increased by cassava hay  supplementation.

It is concluded that cassava hay supplementation improves intake of rice straw, rumen ecology, and digestibility in native cattle.

Key words: Cassava foliage, cattle, digestibility, intake, rice straw, rumen ecology, variety.

Introduction

Native beef cattle are the most important bovine animals on small farms in Lao PDR. The importance of cattle cannot be judged only by their economic contribution from meat, since social, culture and other values such as draught power, transportation and manure are even more important at village level. However, farmers have experienced frequent animal losses through diseases due to very basic causes such as a shortage of feeds both in quantity and quality and this situation is still continuing. Due to the enormous amount of crop residues locally available, there is potential for their use as feed, especially for ruminants (Leng et al 1993).

Cassava or tapioca (Manihot esculenta, Crantz) is grown widely in tropical countries. This plant is well known for its adaptability to poor soil condition, drought resistance and pest tolerance. Usually, cassava is grown for root production and is regarded as a cash crop. However, attention has recently been focused on the potential of the whole cassava crop in livestock production (Preston 2001; Wanapat 2001).  Recently, Wanapat et al. (1997) drew attention to the potential of cassava foliage made into hay,  which combined leaves, stems and petiole, as a feed for ruminants. A more recent approach (Preston 2002) has been to cultivate the cassava plant as a semi-perennial forage, with repeated harvests of the foliage at 2 to 3 month intervals.  Alternatively, the foliage can be harvested at the early growth stage of 3 months and then once or twice more, before leaving the plant to develop the roots for harvest at 8 to 12 months (Wanapat 2001). Ffoulkes and Preston (1978) reported growth rates in fattening Zebu cattle of 800 g/day when fresh cassava foliage was the only protein source in a diet based on liquid molasses-urea  This finding was confirmed by Wanapat et al (1997)  when they showed that cassava hay had low rumen protein degradability,  which would be expected to result in part of the protein escaping the rumen fermentation and thus acting as a source of bypass protein. The use of cassava hay in dairy cattle feeding has been successfully implemented in several ways (Wanapat et al 2000a,b), such as inclusion in the concentrate supplement (Bezkorowajnyi et al 1986;  Wanapat et al 1992), or in a high quality feed block (Koakhunthod et al 2001).

There appears to be no experience in Laos of the use of cassava foliage as feed for ruminants. It was therefore the objective of this experiment to investigate the potential for production of cassava foliage, and its use as hay for supplementation of native beef cattle fed rice straw diets.

Materials and methods

Experiment 1: Comparison of cassava hay yield and chemical composition of local and introduced varieties.

Site of experiment

The experiment was carried out from May 20 to December 20, 2002 on an acid sandy loam soil (pH 4 to 5) in the Livestock Research Centre of NAFRI,  Namsuang, 40 km from Vientiane city.

Land preparation and cassava planting

The land was ploughed well to break soil clusters and to eradicate weeds using a small tractor. At the beginning, fertilizer was applied at 150 kg/ha (N-P-K, 15-15-15). Plots (4 x 8m) were prepared to grow two varieties of cassava (4 plots for each variety). Plant spacing was 90 cm between rows and 60 cm between plants in the row. Cassava stalks of RY72 (from Thailand) and a local variety were cut into 15 cm lengths and embedded in the soil at an angle of about 60º.

Harvesting and determination of yield and chemical composition

The first cutting was at 3 months (August 20, 2002) and was followed by two subsequent cuttings every 2 months. At approximately 9.00 am of the sampling day (when the cassava leaves were free from dew), 4 samples were randomly collected from 4 sites by hand breaking of the stem about 20 to 30 cm above the ground. The samples were weighed and sun-dried and the DM, ash and N were measured using procedures of AOAC (1990). NDF, ADF and ADL were determined by the procedures of Goering and Van Soest (1970). Condensed tannins were estimated by the Vanillin-HCL method (Burns 1971, modified by Wanapat and Poungchompu 2001).

Statistical analysis

All data from the experiment were subjected to analysis of variance using the General Linear Model Procedure of SAS (1998) according to a 2x2 factorial arrangement in Randomized Complete Block Design. (RCBD). Treatment means were compared by Duncan's New Multiple Range Test (Steel and Torrie 1980).from

Experiment 2: Effects of levels of cassava hay (CH) supplementation in native beef cattle fed on rice straw.

Location

The experiment was carried out at the experimental farm of  the Livestock Research Center of NAFRI, Namsuang,  from May to September, 2002.

Animals

Four native bulls, about 2 years old with 150 kg average live weight, were fitted with permanent rumen fistulae. Vaccinations, deworming and vitamin A, D₃, E injections were given before the commencement of the experiment. Each animal was weighed at the beginning and the end of each period.

Experimental design and treatments

The animals were randomly assigned to receive the following dietary treatments according to a 4x4 Latin square design:

• CH0:  Rice straw and rumen supplement (Control)
• CH200: Rice straw and rumen supplement with 200 g /day of cassava hay
• CH400: Rice straw and rumen supplement with 400 g /day of cassava hay
• CH600: Rice straw and rumen supplement with 600 g /day of cassava hay

Housing

The animals were placed in individual pens with permanent roof. Clean, fresh water was available all times during the whole experiment; cleaning of the pen was done daily.

Management and feeding

Rice straw was collected from local farmers and transported to the station. It was offered ad libitum (about 20% above recorded intake). Cassava hay was prepared by harvesting the whole cassava plant 3 months after planting, breaking the stem at about 10cm above the ground. The foliage was chopped into small pieces (2-3 cm) by machine. It was then sun-dried for 2 to 4 days until the leaves became crispy (> 85% DM). It was stored and fed to the cattle according to the respective treatments in two equal parts in the morning and in the afternoon. The rumen supplement contained 190 g rice bran and 10 g urea. It was fed twice daily (7am and 4pm)  in two equal feeds of 100 g each.

Measurements

In each period, the animals were adjusted to the new feeds for one week, after which rice straw intakes were measured daily during a further 3 weeks.  During the last two days of each period, rumen fluid was collected at 0, 2, and 4 h post feeding. Rumen pH was measured immediately using a potable pH meter. Rumen fluid was prepared for later analysis of NH₃-N using the KJELTEC AUTO 1030 analyzer (Bromner and Kennelly 1965) and volatile fatty acids (VFA) using HPLC model 600, with UV Detector (Millipore corp.) (Samuel et al 1997). Blood was collected from the jugular vein from each animal at 0, 2, and 4 h post feeding and was analyzed for urea nitrogen (BUN) by the method of Crocker (1967). Samples of feeds were randomly collected. Fecal samples were collected from the rectum during each of the last 5 days for each period and composited for later chemical analyses. Feeds and fecal samples were analyzed for DM and ash, using procedures of AOAC (1990), and NDF, ADF and ADL according to Goering and Van Soest (1970). Acid insoluble ash (AIA) in feeds and feces was determined by the method of Van Keulen and Young (1977), and was used to calculate digestibility of DM, OM, CP, NDF, ADF and ADL . Condensed tannins (CT) were estimated by the Vanillin-HCL method (Burns 1971, modified by Wanapat and Poungchompu 2001).

Statistical analysis

The data were analysed  using the General Linear Model (GLM) of  the ANOVA option in the SAS (1998) software. Treatment means were compared by Duncan's New Multiple Range Test (Steel and Torrie 1980).

The model was:

Y_ijk = µ + R_i + C_j + T_k + E_ijk

where Y_ijk = Observed value from row i column j treatment k
µ = Overall sample mean
R_i = Effect of row i
C_j = Effect of column j
T_k = Effect of treatment k
E_ijk = Experimental error of the mean

Results and Discussion

Experiment  1: Cassava hay yield and chemical composition of local and introduced varieties.

The fresh matter foliage yield of the variety "RY 72" was  higher than in the local variety at each of the harvests (Figure 1). For both varieties, the yield decreased linearly with time after planting.  This latter result is in contrast with the experience in Vietnam and Cambodia (Preston 2002), where  yield at repeated 2-month harvest intervals was maintained over a 2 year period. The difference probably reflected the fertilizer management which was only at planting time in the present experiment whereas in the experiments reported by Preston (2002), goat manure or biodigester effluent was applied at the rate of about 180 kg N/ha after every harvest.

Figure 1: Fresh foliage yield of two varieties of cassava during three consecutive harvests

There were only minor differences in composition due to variety or harvest interval (Table 2). In general,  the values are comparable with those reported in the literature (Gomez and Valdivieso 1984; Ravindran 1993; Poungchompu et al 2001; Wanapat 2003)..

Experiment 2: Effects of levels of cassava hay (CH) supplementation in native beef cattle fed on rice straw.

The composition of the dietary ingredients is shown in Table 3.

Live weight change appeared to reflect positively the levels of cassava hay that were offered (Table 4). Supplementation with cassava hay increased both intake of rice straw and of total DM. These results are similar to those of Seng Mom et al (2001),  who reported increased intakes of DM and higher live weight gains of local cattle when untreated rice straw was supplemented with fresh cassava foliage. Ho Quang Do et al (2002) observed linear increases in DM intake and N retention in goats fed urea-treated rice straw and increasing amounts of fresh cassava leaves. These reports and the results of the present study confirm the earlier findings of Ffoulkes and Preston (1978), in which fresh cassava foliage supported growth rates of over 800 g/day when added to a protein-free diet of molasses-urea, and lend support to the hypothesis (Wanapat et al 1997) that  the condensed tannins in cassava leaves forms a complex with the protein, so that much of the protein escapes the rumen fermentation contributing amino acids directly to the animal. 

Rumen parameters, ammonium nitrogen (NH₃-N) and blood-urea nitrogen (BUN)

Cassava hay supplementation did not affect rumen pH, rumen ammonia or blood urea (Table 5). This suggests: (i) that the basal diet of rice straw and rumen supplement (providing 10 g urea/day) supplied sufficient rumen ammonia for microbial activity; and (ii) that most of the protein in the cassava hay was escaping the rumen fermentation and not contributing to the rumen ammonia pool..

Rumen ecology

Counts of bacteria increased as did fungal zoospores, while counts of protozoa tended to decrease, as levels of cassava hay were increased (Table 6). Condensed tannins in feeds have been reported to improve rumen ecology, especially enhancing microbial protein synthesis (Makkar et al 1995; McSweeney et al 1999). The mode of action of the condensed tannins  is still to be substantiated; however, if they reduce the protozoal population  then increases in fungal zoospores (Leng 1982) and bacteria (Leng 1989) are expected to be one consequence, with resultant positive effects on rumen  microbial protein synthesis and fibre digestibility.

Digestibility coefficients

Digestibility coefficients increased linearly as cassava hay levels were increased. Wanapat et al. (1997, 2000a) reported similar effects as a consequence of supplementation of cattle with cassava hay.  Part of this effect would be due to the higher digestibility of the cassava hay component of the diet. The decreased protozoal population and enhanced population of fungal zoospores (Table 6) could also have contributed to this effect.

Conclusions

It is concluded that cassava hay supplementation to native cattle, fed a rice straw basal diet and a rumen supplement, improves feed intake, rumen ecology and digestibility.

Acknowledgements

The senior author wishes to extend warmest gratitude to all who have supported the research and development work in this study particularly the Swedish International Development Agency (SIDA) and Swedish Agency for Research Cooperation with Developing Countries (SAREC), through the MEKARN regional project. The National Agriculture and Forestry Research Institute (NAFRI), the Livestock Research Center (LRC) and the Ruminant Nutritional Laboratory of the Department of Animal Science, Khon Kaen University, Thailand, provided research facilities, animals and chemical analyses of samples. The paper is based on research by the senior author submitted in partial fulfillment of the MSc degree in Tropical Livestock Science, Swedish University of Agricultural Sciences.

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