Severe Anthelmintic Resistance in Two Free Grazing Small holder Goat Farms in Malaysia

In one government sheep breeding farm, multiple resistance was reported towards oxfendazole (Benzimidazoles – Bz), levamisole (Imidazothiazoles – Leva), ivermectin (Macrocyclic lactones – ML), with suspected resistance towards moxidectin (ML) [5]. Total anthelminthic failure of all five commercially available anthelmintic drug classes – Bz, Leva, ML and Salicylanilides (Clos) was also reported in five small ruminant government farms in Sabah, East Malaysia [5] and in five small ruminant government farms in Peninsular Malaysia [6].


Introduction
Helminthiasis in small ruminants has been identified as the second most important cause of mortality and morbidity in small ruminants of Malaysia [1]. Consequently, anthelmintic resistance has been reported in the small ruminant farms over the years [2][3][4].
In small ruminant private farms in Malaysia, the occurrence of multiple resistance towards two or more anthelmintics from different drug groups was reported by various authors [3,6]. Since government and private small ruminant farms in Malaysia are actively distributing their animals to other smallholder farmers throughout the country through trading, the severity of this problem is likely to have been widely dispersed.
In 2011, one goat farm located in Ipoh Perak had recorded mortality of 33% per month with worm infection as the main cause despite injectable ivermectin given to the animals once a year. In another farm, mortality of animals was much lower, 13-40% mortality annually even though the animals were never treated with anthelmintics. Thus a study was conducted to evaluate the current status of nematode anthelmintic resistance in these farms, as anthelmintic resistance was never evaluated on these farms and it is suspected to occur at least on one farm.

Materials and Methods
Faecal Egg Count Reduction Test (FECRT) [7] was conducted on 2 goat farms in Ipoh, Perak to evaluate the status of resistance of nematode to four types of anthelminthics; Benzimidazoles (Albendazole, Vetpharm Laboratories (S) Pte. Ltd.), Imidazothiazoles (Levamisole, Bovet Pharmaceutical Ltd.), Macrocyclic Lactones (Ivermectin, Man./Fab: KELA N.V.) and Salicylanilides (Closantel, Janssen Pharmaceutical N.V.). In each farm, animals were divided into 5 equal groups of 8-10 animals and then the animals were treated according to the manufacturers' recommended dose rates based on individual body weight. The animals in the control group were not given any treatment.
In each farm, pre-treatment rectal faecal samples were collected from each animal. The animals in each group were treated, while the animals in the control group were identified and no treatment was given. Faecal samples were subjected to faecal egg count using the McMaster method [8] with one egg counted equivalent to 100 eggs per gram faeces Rectal faecal samples were collected again 10 to 14 days post treatment, for faecal egg count. Faecal culture (MAFF, 1986) was conducted following the faecal egg count by pooling all samples in each farm (pre-treatment) and by treatment groups in each farm (posttreatment) to identify the species of nematodes present. Identification of species was conducted using the identification keys by Manual of Veterinary Parasitological Laboratory Techniques (1971).
Analysis of data to evaluate the status of resistance was conducted based on the calculations outlined by Coles et al. [7]. Resistance to a particular anthelminthic was considered to be present if the reduction in faecal egg count was less than 95% and the 95% lower confidence limit was less than 90%. If only one of two criteria was met, the status was considered as suspected resistance. If the reduction in faecal egg count was more than 95% and the lower confidence limit was more than 90%, the status was considered as susceptible [7].

Managements
Information on the management of the animals in the farms are summarized in Table 1.
Both farms are privately owned farms with animal numbers ranging between 60-90 heads per farm. In both of the farms, the goats were crossbreds Boer and Jamnapari, as the farmers kept various breeds together in their farm since they had started farming. The two farms practised semi-intensive management, where by animals grazed for 4 hours during the day and housed in raised-floor, wooden sheds during the night.
Animals in the shed were supplied with water ad libitum, salt or mineral blocks and one of farm also provided with commercial pelleted feed. Only in one farm (Farm A) the animals were dewormed once a year with ivermectin. Another farm (Farm B) the animals were never dewormed.

Anthelmintic resistance
Farm A was found to be resistant to all drugs tested -Bz, Leva, ML and Clo while Farm B was resistant to all three drugs tested-Bz, Leva and Clo. Leva is still effective in Farm B ( Table 2). The egg counts for each treatment group are given in Table 3

Discussion
Anthelmintic drugs such as benzimidazoles, levamisole and closantel are commonly used in Malaysian goat and sheep farms to control helminthiasis. However, over the past two decades there have been complaints of ineffectiveness of these drugs as farmers can buy these easily from veterinary drug distributers. Investigations by the Veterinary Research Institute have revealed a steady increase in sheep and goats being resistant to these drugs and of late even ivermectin. Anthelmintic resistance survey conducted by Dorny et al. [2] revealed 36% of goat farms to be resistant to benzimidazoles from a survey involving 92 farms locally. It was seen that the strongyles showing resistance to benzimidazoles are Haemonchus contortus and Trichostrongylus spp. Other workers, have reported up to 75% of goat farms to be resistant to benzimidazoles [3,8]. In this study, both farms showed critical resistance to benzimidazoles and ivermectin indirectly indicating that these 2 drugs may have been used frequently and excessively in goats. According to Coles et al. [8] Farm 2 had a susceptible worm population which could be controlled with levamisole. In a situation like this, alternative methods of worm control such as rotational grazing, or herbal remedies can be used to alleviate the helminthiasis problem. In Malaysia, commercial farms are advised to practise zero grazing or cut and carry feeding to reduce worm infestation as drug therapy with a less than effective product would considerably increase costs. There is tremendous pressure to turn towards ecofarming, reduce drug use and implementation of sustainable practises to control helminthisis in small ruminants, the biggest cause of production losses in the tropics.