Effect of grass or cassava foliage on growth and nematode parasite infestation in goats fed low or high protein diets in confinement

Seng Sokerya and T R Preston*

University of Tropical Agriculture (UTA) Cambodia 
PO Box 2423, Phnom Penh 3, Cambodia.
kerya@mekarn.org
*UTA-TOSOLY - Finca Ecológica
Morario - Guapota - Santander del SurColombia      
regpreston@utafoundation.org

Abstract

Two experiments were conducted to find out the effect of cassava foliage compared with grass on the growth rate and parasite infestation of growing goats. 12 crossbred goats, treated with  Ivermectin before starting, were used in experiment 1 which lasted 80 days. There were 3 treatments according to the source of forage (Cassava alone, Cassava + Grass [50:50 percent in DM] and Grass alone) as supplement to a basal diet of brewer's grains. Experiment 2 was with 16 local goats allocated to 3 treatments with no initial injection of Ivermectin (Cassava alone, Cassava + Grass [50:50 percent in DM] or Grass alone) and a 4th treatment of grass alone with injection of Ivermectin at the start. In this experiment the basal diet was wheat bran. In both experiments, the forage supplement supplied about 50% of the diet DM.

The goats given diets containing cassava foliage had faster growth and better feed conversion. EPG were either lower on cassava-supplemented diets compared with the grass alone (Experiment 1) or declined with time from high initial values (Experiment 2). DM digestibility was apparently depressed on the cassava, compared with the grass, diets but this negative nutritional effect appeared to be more than compensated by the much higher protein intakes with cassava.

It is suggested that the better performance on the cassava diets was due to the higher protein intake and that the protective action against nematode parasites was due to the content of condensed tannins.

Key words: Cassava foliage, condensed tannins, digestibility, EPG, goats, growth, nematodes

Introduction  

Drug resistance has become an important issue in small ruminant husbandry when anthelmintics are applied at high levels and increasing frequency and with inappropriate doses (Pandey et al 2001; Chartier et al 2001; Chandrawathani et al 1999). The use of natural substances is becoming preferable and may offer better control than using chemical compounds to treat parasitised animals (Orr, No date and Chandrawathani 2001). This seems more appropriate, more practical and sustainable for the smallholder farmers as the use of natural substances is the traditional way of dealing with diseases in rural areas in developing countries.

Condensed tannins are secondary plant compounds that have inhibitory effects on digestive processes (Barry and McNabb 1999). However, goats can tolerate high levels (up to 2.7 g/kg live weight) without suffering ill effects (Silanikove et al 1996) and have superiority in dealing with tannin better than the sheep (Narjisse et al 1995). There are also reports that at high concentrations they have anthelmintic properties against nematode parasites (Khan Diaz-Hernandez 2000; Butter et al 2000). However, nutritional level especially with protein is considered to be an important factor in conferring resistance to parasites (Nolan 1999).  Additional protein supplementation enhanced parasite control as well as giving beneficial responses in production (Knox 1996). It has been observed that drenching with anthelmintic did not result in better growth if the nutritional level also was not improved (Pralomkarn et al 2001), as there was no significant difference in growth rate between control and drenched animals. The interaction between these two factors was suggested to be investigated under lower nutritional conditions such as in a village farm situation.

Cassava foliage is relatively rich in condensed tannins (Wanapat et al 1997), and feeding it in the form of sun-dried hay has been reported to reduce faecal egg counts in grazing buffaloes  (Netpana et al 2001; Granum et al 2003). When goats housed on slatted floors in full confinement were fed fresh cassava foliage as a forage supplement to brewer's spent grains, growth rates were faster and faecal egg counts much lower than when cut grass was the supplement (Seng Sokerya and Rodríguez 2001).

On the basis of the above observations the objectives of the present study were:

1.     To determine the source of infection from internal parasites in confined goats

2.     To find out the direct effect of condensed tannin in cassava foliage on nematode  parasites

3.     To evaluate the effect of the protein level on the growth rate and parasite infestation of goats receiving cassava foliage (expected to inhibit parasite infestation) or grass (a potential source of infestation).

 

Materials and methods

Location

The experiments were conducted from April to October 2002 at the ecological farm of the University of Tropical Agriculture (UTA), situated in the campus of the Royal University of Agriculture, about 12 km from Phnom Penh the capital of Cambodia. This region is located in a monsoon tropical climate where mean air temperature is in the range of 33 to 40 °C in April to May and 20 to 29 °C from June to December. 

Housing

The goats were confined individually in wooden pens with 1*1.5 m floor area, fitted with raised slatted floors about 1.2 m higher from the ground in a building with open sides and a thatch roof. The feeders are situated on the outside of the pen, where the animals can put their head to eat or drink. This also facilitates the feeding and collection of feed residues (Photo 1).

 

Treatments, animals and design

Experiment 1:

The three treatments were different forages, or combinations of forages, as supplements to a basal diet of Brewer's spent grains. The supplements were:

             G:    Cut natural grass

             C:    Cassava foliage

             GC: A mixture of grass and cassava foliage (50:50 DM basis)     

There were four replications in a randomized block design (CRD), after blocking the animals on the basis of live weight and sex. The experimental period was 80 days. 12 crossbred Bach Thao goats (6 males and 6 females) were used in this experiment with the average body weight of 20 kg for males and 16 kg for the female goats, and between 5 to 8 months of age. All the animals were selected from the goat herd in the Ecological farm of UTA. They were treated with Ivermectin (MERIAL, Merck, Sharp and Dohme, BV, Netherlands), before starting the experiment to be sure that they were free from parasites. There was an adaptation period of one week before starting the experiment to accustom the goats to the housing and the feeding system.

Experiment 2:

In this case, 4 treatments were arranged in a CRD design using 16 goats and a basal diet of wheat bran. The treatments were:

C:  Cassava foliage

CG: Mixture of grass and cassava foliage (50:50 DM basis)

G: Grass

Gt: Grass + injection of Ivermectine at the beginning of the experiment.

 

Thus 3 treatments followed those in Experiment 1 (but without anthelmintic), while the 4th treatment (Gt) was the same as "G" but with injection of the anthelmintic (Ivermectin). The basal diet of brewer's grain was also replaced by wheat bran which has a lower protein content to allow a better observation on the effect of the supplementation. The animals in each treatment were blocked according to EPG level in the beginning of the trial. The highest fecal egg count animals were allocated to the cassava treatment (C), and the lower ones to the grass treatments (Table 1). There were 4 replications (individual animals) in each treatment and the experimental period was 70 days.

 

 

Sixteen female goats of the local breed were used. The body weights were in the range of 8 to 12 kg and the ages between 3 and 5 months of age. All the animals were purchased from local goat farms in the area around Phnom Penh city (Theng Kouch et al 2003). In this experiment, a longer period of adaptation (21 days) was necessary because the goats on the "C" and "CG" treatments were slow to adapt to the cassava foliage.    

Feeding and management

Experiment 1:

Brewer’s spent grain was used as the basal diet at a restricted level, of 50% of the expected ad libitum intake, which was estimated to be about 4% of liveweight on dry matter basis (Peacock 1996). The supplements were foliage from cassava, cut natural grasses or the mixture of the two given on a 50:50 (DM basis) ad libitum. The feeds were offered 2 times per day in the morning about 10 am and in the afternoon about 3 pm. Water was always available. Cassava foliage was harvested daily from semi-perennial plots in the ecological farm of UTA. The foliage (leaves, petioles and green stems) was from re-growths harvested regularly at 50 to 80 day intervals (Preston et al 2001), the hard stems being cut about 50cm from the ground for the first harvest and 5 to 10cm from the point of the first cutting for the next harvest. The natural grasses were collected in the field around the area of the ecological farm every day in the morning before feeding. The fresh brewer’s grain was received every two weeks from the local brewery and was immediately ensiled in closed concrete containers to preserve it from rancidity. 

Experiment 2:

Feeding and management were similar to the procedures used in Experiment 1, except that wheat bran replaced the Brewer’s grain and the feeding level was restricted to 200 g (air-dry basis) daily. The wheat bran was received monthly from the local wheat factory and kept in feed storage at the Ecological farm.

Measurements

Experiment 1:

Live weight was recorded at the beginning, every 10 days and at the end of the experiment. The amounts of feed offered and refused were measured and recorded daily, separately for the basal diet and the supplements.  Representative samples of feeds offered and refused were analysed for dry matter by micro-wave radiation (Undersander et al 1993) and nitrogen content (AOAC 1990). The cassava foliage was analysed for the concentration of HCN (AOAC 1990) and condensed tannins (Burns 1971). After weighing the animals, faecal samples were taken directly from the rectum to determine the concentrations of the parasite eggs (EPG).    

EPG counting procedure: 4 g of faecal sample were ground and mixed with 56 ml of flotation fluid (a saturated salt solution in water). After filtering through a “tea strainer”, a sub-sample was transferred to both compartments of a McMaster counting chamber and allowed to stand for 5 minutes. All helminth eggs were counted under a microscope at 10x magnification and multiplied by 50 to yield the EPG (Eggs per gramme) of faeces (Hansen and Perry 1994).                                                                

Experiment 2:  

The measurements were similar to those employed in Experiment 1. In addition, at the end of the trial, one goat from each treatment was slaughtered to determine the total worm burden in the intestinal gut. The eggs in the faeces were cultured to identify the species of the infective larva using the faecal sample from the slaughter animals. Digestibility of dry matter, organic matter and nitrogen was determined by taking samples of feed, feed residue and faeces over 5 days at the end  of the trial, bulking them to obtain representative samples, which  were then analysed for acid insoluble ash using the method of Van Keulen  and Young  (1977). The faeces samples were taken from voided excreta under the individual pens.

Data analysis

All the experimental data were subjected to analysis of variance (ANOVA) by using the General Linear Model (GLM) of the MINITAB software (Release 13.31, 2000). The model was: 

Yi = µ+ Ti + ei  
where  

Yi = Dependent variable

 µ = overall mean

Ti = treatment effect

ei = random error

 

Results

Chemical composition of the diets

Experiment 1:

Experiment 2:

The values for composition of the cassava and grass were similar to those in the first experiment (Table 4). For wheat bran the protein content was typical of literature values (FAO 2003). Values for condensed tannins (CT) and HCN on representative samples were 4.15 % and 653 mg/kg of DM, respectively.  

Feed intake and growth rate

Experiment 1:

The actual proportions consumed of cassava foliage and cassava foliage + grass were close to the planned proportions of 50% of the diet DM (Table 5).  Total DM intake expressed as a percentage of live weight, and daily live weight gain, tended to be higher (P=0.16) for the treatments with cassava foliage compared with grass alone. Feed conversion was poorer on grass alone with no differences between cassava and cassava + grass. Protein intake as percent of live weight was highest on cassava and lowest on the grass supplement.

 

Experiment 2:

DM intakes did not differ among treatments and were of the same order (as % of LW) as in Experiment 1 (Table 6).  Protein intake, as percentage of live weight was higher on the cassava diets (C and CG) than on the grass diets (G and Gt). However, growth rates were much lower and feed conversion poorer than in Experiment 1. 

Growth rate was higher on cassava alone than on the other treatments combined (mean difference 14.5±4.6; P=0.057).  The same was true for DM feed conversion which was better on cassava alone than on the other combined treatments (mean difference 5.29±1.7; P=0.056) (Figure 1). There was no beneficial effect on performance traits from the anthelmintic treatment at the beginning of the trial (G vs Gt).

Figure 1: Mean values for live weight gain and feed conversion for goats supplemented with cassava alone (C)
versus the combined data for the other diets (CG, G and Gt) (Experiment 2)

Digestibility

Experiment 2:

DM intake was higher and apparent digestibility coefficients lower when cassava alone was the forage supplement compared with the grass treatments (Table 7).  Faecal DM content was higher, as was faecal pH, for goats given the diets with cassava (C and CG) compared with no cassava (G and Gt).  

 

Faecal Egg Count

Experiment 1:

The changes in EPG during the experiment showed marked differences between treatments with increasing EPG on the grass treatment and negligible values for the treatments involving cassava foliage (Figures 2 and 3). However, even on the grass the level of infection was quite low.

Figure 2: Trends in EPG before (day 0) and during the experiment after injection of  invermectin on day 1

 

Figure 3: Mean values for average EPG in goats supplemented with cassava foliage alone,
 mixed with grass or grass alone (Experiment 1)

 

Experiment 2: 

EPG counts were high on the cassava and cassava + grass treatments at the beginning and showed a steady decline during the experiment from about 4000 to 5000 in the first 30 days to about 1500 after 70 days (Figure 4). The goats on the supplement of grass only had low EPG at the beginning and maintained these values throughout the trial. Those treated with invermectin had nil EPG for the first 60 days and then began to show signs of re-infection (range of EPG from 150 to `1200 on day 70).  

 Figure 4: Trends in EPG  during experiment 2  

Examination of the larvae cultured from the eggs in the faeces samples from 4 goats (one on each treatment) showed that the worms were almost entirely of the Haemonchus contortus species.
  

Discussion

Growth rate

The faster growth rates and better feed conversion in Experiment 1 probably relate to the breed and origin (Bach Thao cross goats from UTA in Experiment 1 compared with native goats purchased from farmers in Experiment 2), the heavier initial body weight and the higher protein content of the diet in Experiment 1, and the fact that in Experiment 1 the goats were accustomed both to confinement and to eating cassava foliage before the the experiment began. The latter point was evident from the longer time needed to adapt to the cassava foliage in Experiment 2, while feed refusals of the cassava foliage in this experiment were also relatively higher than in Experiment 1. Considering both growth rate and feed conversion, the data from both experiments indicate better goat performance with the high level of cassava foliage as the supplement, which is in agreement with the earlier findings of Seng Sokerya and Rodríguez (2001). Nguyen Kim Lin et al (2003) also reported better growth of goats when fresh cassava foliage rather than grass was the forage supplement to a diet of rice bran.

Digestibility

The results for DM digestibility (70%) are only slightly lower than the value (73%) reported by Theng Kouch et al (2003a) who fed a  sole diet of cassava foliage to goats with the same feeding system (foliage placed in the feed trough) as in our experiment. Tran Thi Thu Hong (2002) fed 100, 75 and 50% cassava to goats, together with wheat bran (on the 75 and 50% cassava diets), and reported DM digestibilities of 79.3, 76.3 and 78.3%, respectively. It is relevant to note that this researcher fed the cassava as a hanging bunch of foliage, a feeding method that was found to result in higher intakes and higher DM digestibility (81%), compared with feeding the cassava foliage in the feed trough (73%) (Theng Kouch 2003a). Ho Quang Do et al (2000) fed up to 47% of cassava foliage to goats replacing rice straw. The reported DM digestibility for the straw alone was 36% and for the diet with 47% of cassava was 57%. Even without the expected positive interaction from the presence of the cassava foliage with a nutrient-poor substrate such as rice straw (see Guttierrez 1978), the calculated digestibility (by difference) of the cassava foliage alone would have been 76%.

The question could be asked: why was growth and feed conversion better with cassava foliage supplement than with grass even though digestibility was higher on the grass? The most likely explanation is the much higher protein intake on the former (8.04 g protein/kg live weight) than on the latter (5.13 g protein/kg live weight). A high level of protein nutrition is also important in developing natural immunity against nematode parasites (Nolan 1999). 

The lower apparent digestibility coefficients recorded for the goats fed the high cassava supplement (50% of DM intake), compared with those receiving grass, appear to be in conflict with the data for growth rate and feed conversion, which favoured the high cassava treatment. However, a negative effect on digestibility has been reported by many workers when they fed forages with high levels of condensed tannins to small ruminants (Romero et al 2000; Silanikove et al 2001; Mcsweeney et al 2001; Feutos et al 2002; Barry and McNabb 1999) so presumably it was the condensed tannins in the cassava that were responsible for the depression in digestibility on the cassava as opposed to the grass diets. 

Faecal egg count

The data for worm egg counts support the earlier findings of Seng Sokerya and Rodríguez (2001), with much lower EPG on the cassava supplement in Experiment 1, and a steady decline from initial high values in Experiment 2.  The difference was that the degree of infestation was much less in Experiment 1 than in the study of Seng Sokerya and Rodríguez (2001). In Experiment 2, the decision was taken deliberately to block the goats according to initial EPG counts, on the basis that this would prove if there were compounds (eg: the condensed tannins) in the cassava foliage that would act as an anthelmintic directly affecting the parasite. The steady decline in EPG on both the cassava alone and the mixed cassava and grass diets would appear to support that decision. Surprisingly the EPG on the grass supplement in Experiment 2 remained low throughout the experiment, which contrasts strongly with the findings in Experiment 1 where the EPG (following invermectin treatment) steadily increased with time.  It is possible that the grass used in Experiment 2 did not contain infective material as it was cut at a higher level from the ground, compared with the practice adopted in cutting the grass in Experiment 1 (which was cut at ground level). This finding is similar to the result from the study by Nguyen Kim Lin et al (2003) on the effects of the cutting height of the grass fed to growing goats in North Vietnam. The faecal egg count was about 2 times higher when the grass was cut low compared with when it was cut high.  Growth rate was also better when the grass was cut high rather than low.

These observations are supported by the findings of  Coffey et al (2001), who showed that when the grass was tall the infective nematode larvae did not climb up to the top of the plant.  It is known that the infective larvae migrate vertically on plants via the moisture film (Niezen et al 1998). These authors indicated that the number of infective larvae that successfully develop and migrate up the stems of the herbage (to be consumed by host animals) can be influenced by pasture-plant species, and that some plant species might have thicker water films than other plants. This migratory behaviour of the infective larvae could also partially explain why the goats in experiment 1 that consumed only cassava foliage had negligible levels of EPG, as it is unlikely that the larvae would climb the stems of the cassava.

Considering the results of the two experiments, together with the findings of Seng Sokerya and Rodríguez (2001), it would appear that there is evidence that cassava foliage contains compounds (presumably the condensed tannins) that have an anthelmintic effect against nematode parasites in goats. In this respect there are many reports in the literature that ascribe such an action to the presence of condensed tannins (Coop and Jackson,  No date; Granum et al 2003; Butter et al 2000; Kabasa et al  2000; Molan et al 2002; Niezen et al 1996; Kahn et al 2001).

Other indirect effects of cassava foliage could be the higher level of protein as compared to grass (Tables 4 and 7), and the expectation that the tannins present in cassava foliage will enhance the supply of essential amino acids to the small intestine (Wanapat 2003). The other advantage of cassava foliage compared with grass is that the infective larvae are unlikely to migrate up the stems of a shrub plant such as cassava. There are many reports in the literature that tannins (in a moderate concentration of 2 to 4%) increase the availability of protein in the small intestine of ruminants, and that this indirectly improves host resistance and resilience to nematode parasites (Barry and McNabb 1999; Kahn and Diaz-Hernandez 2000; Kahn et al 2001). The importance of the protein nutrition of the host animal as a factor enabling it to overcome parasitism has been emphasized by many authors (Coop and Kyriazakis 2001; Haile et al 2002; Nolan 1999; Waller 1997; Meissner and Paulsmeier 1995; Coop and Holmes 1996).

Conclusions

Diets for growing goats containing cassava foliage, and either brewer's grains or wheat bran,  supported better growth and feed conversion, and exhibited protective mechanisms (presumably due to the content of condensed tannins in the cassava)  against nematode parasites, than similar basal diets supplemented with freshly cut grass.

DM digestibility was apparently depressed on the cassava, compared with the grass, diets but this negative nutritional effect appeared to be more than compensated by the much higher protein intakes with cassava.

 

Acknowledgements

The present experiment is part of a study on the use of cassava foliage as a feed and natural anthelmintic source for goats. It was partially supported by the MEKARN project, financed by the SIDA-SAREC Agency, and the regional project “Development and Testing of an Integrated Approach to the Control of Gastro-Intestinal Parasites of Small Ruminants in South and South East Asia (TAG 433)".  The authors express their gratitude to the staff of the Ecological Farm, of the University of Tropical Agriculture Foundation, for help with the experiment. Thanks are also expressed to Dr Julio Ly, visiting scientist, for advice and help with the editing of this paper, and to Mr. Pok Samkol for analytical assistance in the laboratory of the Ecological Farm. The research reported here was submitted by the senior author as partial requirement for the MSc degree in the Swedish University of Agricultural Sciences, Uppsala.
 

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