AN ABATTOIR STUDY ON THE PREVALENCE OF GASTROINTESTINAL NEMATODES OF GOATS IN THE DRY ZONE OF SRI : LANKA

During a 12 months study (January to December 1996) gastrointestinal , tracts of 218 crosshred goats representmg the diy zone of Sri Lanka were collected and examined for the presence of gastrointestinal parasites. Two hundred and seventeen (>99%) of the animals examined were infected with one or moi-e spec~es of nematodes. The worm hurden was classified hased on the number of adult worms, one hundred and twenty an~mals (55%) had a low to moderate worm hurden (0-1000) and 98 (45%) had a high worm hurden (>I()()()). Five species of nematodes we1.c found in the ahomasum and intestines. Tliey were O~sophogostonr urn colrrrrr binrrrrnr (8)5(%), Hnrnrorrrh~rs col~for tus (XI%), Zkichosfron~dus colr/hrrforrnis (76W), 'IFirlrosfro~rq~~lus ( I X P L (5I)%) ancl'121churr.s or~rs (59%). The higl>est of the mean wo in hurden was due to small intestmal nematodes (1122) while large intestinal nematodes accounted ior the lowest (34). The mean hLal number was 1751. The pattern of woi-m hurden was bimodal and marginally seasonal.


INTRODUCTION
Goats are an important source of food and income for smallscale farmers within rural communities of many tropical and sub tropical countries of Asia and ~f r i c a ." Sri Lanka, an island in the Indian Ocean with approximately 65,000 square kilometers land area has a goat population of around 500,000 of which about 65 per cent are distributed in the Dry (average annual rainfall: <I250 mm) and Dry Intermediate (average annual rainfall: 1250-2000 mm) Zones of the country.It is estimated that annually about 125,000 animals managed under an extensive system within these areas are slaughtered to meet the goat meat requirements of the country.
Gastrointestinal nematode infections in goats have been recognised as a major constraint to the development of this livestock enterprise in many developing 25 countries of the tropics.Studies in Africa and South and South East Asian Corresponding author countries have shown that worms of the genera Haem,onchug ?Fich.ostrongylu,s and Oesoph,agostontum are the common gastrointestinal nematodes affecting small 2,15,18,24 ruminants.
Further it has also been noted that Haemon.chu,scontortus is the most pathogenic species responsible for a marked growth retardation and death.
The epidemiology of trichostrongylid worms in goats has been studied in n o India, pakistan17, ~a m b i a " ) , ~a u r i t a n i a ' ' , Zimbabwe1' and Saudi ~r a b i a .' Parasitologists rely on epidemiological data of gastrointestinal parasites to understand the complex host-parasite-environment relationship in order to establish inexpensive, sustainable control strategies, which need to be communicated to farmers.Control programmes based on a sound knowledge of parasite epidemiology produce maximum benefits while lowering the risk of anthelmintic resistance.' In common with other tropical countries, goat farming plays a significant role in the rural economy of Sri Lanka and gastrointestinal nematode infections are recognized as a major cause of morbidity and m~rtality."~:'According to Van Aken et 2b al. H. contortus and Oesph,agostomunt columbian.untwere the only species of nematodes present in a government goat-breeding farm in the Northwestern part of Sri Lanka.Nonetheless, a vast majority of goats are managed by traditional small-scale rural farmers in the Dry Zone where little is known of the gastrointestinal nematodes and their effects on animals.Anthelmintic therapy is not generally practised to control gastrointestinal parasites.If used, i t is done in a n indiscriminate and a d hoc manner since very little information is available on the epidemiology of nematodes infecting the gastrointestinal tract.The objective of this study was to identify the spectrum of gastrointestinal nematodes of goats in the Dry Zone of Sri Lanka, determine their prevalence levels and investigate the distribution in relation to months and season.

METHODS AND MATERIALS
a. Study Area: Samples for this study were collected from goats that originated from different locations of the area designated as the Dry zone; North-western, Southern and North-central Provinces, of Sri Lanka where the average annual rainfall is generally 4 2 5 0 mm and temperature varied from 21-38°C (Meteorological Department, Colombo).The climate is bimodal, characterized by a warm rainy season from October to January and short dry season from February to March.The month ofApril is usually rainy and there is a long dry season from May to September.b.Animals: All animals used were of the local or indigenous breed (12-24 months of age) that were typical of goats raised in the Dry Zone.In general, the animals in the Dry Zone were managed extensively, being turned out to browse in the shrub jungle, communal grasslands or along the road sides during the day for an average period of 6-8 hours and housed a t night in stilted sheds fned with a wooden slatted 11.13,21 floor or mud$loor.
During the long dry season the nutritive value of the vegetation declines to its lowest levels and the animals are then subjected to substantial nutritional stress as no supplementary feeding is provided.Significant deviations from the generally found management were very rarely encountered.
c. Sample collection: Material for the study was collected monthly from goats in the aforementioned areas that were slaughtered a t the Colombo municipal abattoir during the 12 month period extending from January to December 1996.On each occasion, 15-20 gastrointestinal tracts were collected and processed to determine the worm burden.The origin of goats also was recorded a t the time of sample collection.
d. Recovery of worms: At slaughter, the alimentary tract from the distal oesophagus to the rectum was carefully removed from the carcass after ligatures were placed at either end.To prevent the mixing of abomasal and intestinal contents, further ligatures were placed a t the pyloric/duodenal junction, between the small and large intestines and a t the proximal end of the caecum.The three segments of the gastrointestinal tract i.e. abomasum, small and large intestines were then separated at the ligatures and processed individually for the estimation of worm burden as described by Ritchie et a1.22The abomasal mucosa was scraped with glass slides and the scrapings digested in pepsin/HCl mixture a t 4 2 ' ~ according to a method described by ~e r l i c h l ~f o r the recovery of mucosal larvae.
e. Statistical An,alysis: Worm burdens were subjected to one way analysis of variance using a computer statistical package (Minitab 10.1 release, Minitab Inc., State Collage) followed by a between month comparison using the Tukey test.Worm burdens during the months ofApril and May were not included in the analysis since low number of samples were collected during these months which precluded any meaningful comparison by the Tukey test.Before analysis, the worm counts were log transformed in order to stabilize the variance.Comparisons were considered significantly different a t P<0.05.

RESULTS
Around 45% of the examined animals originated from the North-Western Province, particularly from Puttalam and Chilaw and around 40% of the animals were from the Southern Province, particularly from Hambantota.The rest of the animals originated fromiarious locations of the North-Central Province.
A total of 218 gastrointestinal tracts were examined over the 12 month period which included both the wet and dry seasons.An overwhelming majority (217 animals; 99%) of the goats examined were infected with one or more nematode species which included 0. columbianum (88%), H. contortus @I%), '12.ichostrongylus coluhriformis (76%), 1: axei (59%) and Dichuris ovis (54%).Two hundred and six animals (94%) were infected with more than one gastrointestinal nematode.The abomasa were infected with H. contortus and T axei, the small intestines were infected with only I: colubriformis and large intestines were infected with both 0. columbianum and T ouis.The prevalence, mean and quantitative range of gastrointestinal nematode infections in the abomasum, small and large intestines are given in Table 1.The average worm burden was greatest in the small intestine followed by the abomasum and then the large intestine.None of the digested abomasal scrapings revealed the presence of mucosal larvae.The seasonal variation of the worm burden in the different parts of the gastrointestinal tract in relation to prevalence, mean and quantitative range is shown in Table 2.Although the overall prevalence of gastrointestinal nematodes in the various segments of the alimentary tract was not markedly different between the seasons, the overall mean worm burden was high during the wet season and reflected the increase in worm counts, particularly of the abomasum and small intestine.The frequency distribution of worms in the three segments of the gastrointestinal tract examined is shown in Table 3.Of the 218 large intestinal tracts, 91 percent harboured less than 100 worms while 76 percent of the abomasa had parasites ranging from 100 to 10,000.The monthly fluctuation of the abomasal, small intestinal and large intestinal wormburdens is depicted in Figure 1.The total worm burden showed a bimodal distribution, which was characterized by an increase in the worm counts beginning from November with a peak in February followed by a gradual decline up to May.The latter was followed by a second increase in which a peak was observed in July followed by a decline in October.Significantly lower total, abomasal, small intestinal and large intestinal worm burdens were recorded during October (p<0.001).The small intestinal nematode counts mirrored the trend of the total worm burden during the year.The large intestinal and abomasal worm burdens on the other hand followed a bimodal pattern in which the second peak was similar (July) to that of total worm burden but the first peak was in April for large intestinal worm burdens and December, for abomasal worm burdens.observation however cannot be compared with similar studies carried out elsewhere in the tropics since the conditions of feeding, management and other factors, which influence the worm burden may be different.
According to Hansen and perry12 an average abomasal worm burden of ,500 for sheep is considered an infection of moderate severity.In the present study the average abomasal worm burden was 595, but i t is not possible to describe the severity of the infection since the relationship between the worm burden and the degree of the infection in goats has not been defined.The extensive system of management in which large numbers of animals are allowed to browse in limited communal grazing lands and the absence of a planned control programme are likely to be the causes responsible for the high worm burden noted in this study.
In the present study, two abomasal nematodes, one small intestinal nematode and two large intestinal nematodes were recorded.In an earlier study, Weilgama and perera2' noted Haemonchus as the most prevalent genus of nematode affecting goats in a Dry Zone farm.In a later study a t the same location, Van Aken et a ~. , ' ~ recorded both Haemonchus and Oesoph.ogostomurn, to be the most common genera of gastrointestinal nematodes.The findings reported herein confirm the latter observations t h a t these genera were the most prevalent nematodes but differs in that there were other species such as ?: colubriformi.~,Z' !axei and ?: ovis which were not earlier reported.The goats examined in the present study were from a wider geographical area of the Dry Zone and therefore it is not surprising that a greater spectrum of parasites were encountered.Several studies in ~f r i c a n ' ~" ~ and Asian countries7"') have also indicated Haemonchus and Oesophogostomum to be the most prevalent gastrointestinal nematode species present in goats.

Many
have reported that the worm burden in domesticated ruminants follow a seasonal pattern where the infection is higher during the wet season compared to the dry period.Although a seasonal rainfall pattern has been described for the Dry Zone with little variation among different locations within this zone, the distribution of the worm burden was only marginally seasonal.Based on the general rainfall pattern described for the area under study, the magnitude and prevalence of gastrointestinal nematodes during the wet season was not significantly higher than that of the dry season.The relatively high worm burden during the dry period may also be attributed to the low nutrition during this period that enhances the build up of the parasitic infection in the gut.Studies in cattle have demonstrated that low pasture availability during the dry period together with an absence of supplementary feeding leads to a lowering of immunity 4.28 resulting in a comparatively high worm burden.Similar observations have also been supported through experimental Haemon,chus infection in sheep where animals maintained on a low nutritional plane had a significantly higher worm

11 ;
burden compared to the controls.In a recent study in goats, Blackburn et al.',