Parasite control practices in Ontario sheep farms

MILTENBURG, C.; BAKELAAR, A.; MENZIES, PAULA; FERNÁNDEZ, ALICIA SILVINA; PEREGRINE, ANDREW

Congreso; 6th International Sheep Veterinary Congress; 2005

INTRODUCTION: The Canadian sheep population in 2002 was 1.3 million, with Ontario having the largest proportion at 27%, located on approximately 4,200 farms. However, no information is currently available on the parasite control methods used by sheep farmers in Ontario. In order to achieve optimal control of gastrointestinal nematodes, it is important to characterize the current practices used by Ontario sheep farmers and to determine how these practices may be improved. Development of anthelmintic resistance is a potential threat for sheep enterprises, but the risk of its development in Ontario is not known. MATERIALS AND METHODS: In May 2004, invitations to participate in the project were mailed to 500 randomly selected sheep farmers, whose enterprises were located in central or western Ontario and who were listed in the Ontario Sheep Marketing Agency database. A total of 167 responses were received. Sixty-five producers accepted the invitation to participate; of those, 58 met the study enrolment criteria of grazing all or part of the sheep flock during the grazing season. During the summer of 2004 a questionnaire was administered by an on-farm interview to collect information on parasite control practices. This questionnaire was pre-tested prior to its use in the study population and gathered information on the general farm structure and specifics of parasite control practices used the past year. It also queried on-farm evidence of gastrointestinal parasitism and/or anthelmintic resistance in the flock. All information was entered into a database for analysis. RESULTS: Flock size ranged from small hobby farms to large commercial flocks. Of the 58 flocks visited, 5 had fewer than 20 breeding ewes, 18 had 20-49 breeding ewes, 12 had 50-99 breeding ewes, 20 had 100-300 breeding ewes, and 3 had more than 300 breeding ewes. The number of anthelmintic treatments administered by producers to adult sheep ranged from 0 to 6 treatments (median = 2) for the twelve-month period prior to visit. Six producers had not treated their sheep with any type of synthetic anthelmintic during this period. Of the remaining producers who had (n = 52), 47 used ivermectin at least once. For those 52 farms, a total of 122 anthelmintic treatments were recorded for the 12-months period, 96 of which were ivermectin, 16 were fenbendazole, and 10 were albendazole. Currently, ivermectin and levamisole are the only anthelmintic licensed for use in sheep in Canada. However, levamisole is no longer available for purchase. Even so, anthelmintics belonging to more than one drug class were used on 17 of the 52 farms. Thirty-five producers had used only one class of anthelmintic, of which 30 had selected ivermectin exclusively. Amongst farms, there was little consistency in either frequency or timing of treatments given. Fifteen percent of treatments were administered between December and March, when there is usually little need to treat adult sheep in Ontario. For the twelve-month period prior to the visit, the number of anthelmintic treatments administered to lambs on the 58 farms ranged from 0-6 (median = 1). A total of 28 producers did not treat lambs with any type of synthetic anthelmintic, even though 17 of these producers maintained lambs at pasture. Of the 67 treatments administered to lambs on the remaining 40 farms over this period, 42 were ivermectin, 20 were fenbendazole, and 5 were albendazole; 17% of treatments were administered between December and March. Data gathered on the method of administration of anthelmintics indicated 31 producers used a drench gun. Of these producers, 22 reported their drench gun had never been calibrated to ensure the accuracy of dosing. Only 4 producers calibrated their drench gun regularly. With respect to dosing of animals, 38 of 52 producers determined the dosage by estimating the weight of animals on an entire flock basis. The remaining producers dosed animals on the basis of individual (n = 1), or small group weights (n = 11), or used the breed average (n = 2). Faecal monitoring to evaluate the efficacy of anthelmintic programs had been carried out in 15 of the 58 flocks during the twelve-month evaluation period. New arrivals to the flock during the previous year from an outside source were reported by 29 of the 58 producers (lambs, ewes or rams). Sixteen of these producers neither dewormed, nor observed a quarantine period prior to introducing new animals into the flock. All producers that quarantined arrivals, did so for a minimum of 10 days. All producers that dewormed new arrivals used ivermectin. Only 6 of 58 producers suspected resistance to an anthelmintic in their flock. However, in none of these instances was the resistance confirmed by either faecal examination or necropsy. DISCUSSION: These data indicate that there is a large variation in the anthelmintic programs used in Ontario farms. The wide range in frequency of anthelmintic treatments given, the discrepancies in ensuring accuracy of dosing and the varied anthelmintic programs for new arrivals demonstrate a lack of standardization in the parasite control programs used by sheep producers. Surprisingly, even though regular faecal monitoring for parasite eggs is required to evaluate the need of treatment, success of treatment and anthelmintic resistance, only a small proportion of producers did so. The general reliance on use of ivermectin (73% of treatments given to lambs and ewes) and the lack of use of other anthelmintics on many farms is of concern with respect to the development of anthelmintic resistance. In addition, although 10% of the producers believed they had a problem with anthelmintic resistance, active precautionary measures to prevent this threat were practiced by only a few producers.