Use of anthelmintics by New England sheep producers.

Six hundred and sixty-five New England sheep producers responded to a postal survey on management practices, anthelmintic use, and the perceived failure of anthelmintics to control nematodes. Although the average farm had 34.8 lambs and 29.8 stock sheep, 59.8% and 50.3% of the total number of lambs and stock sheep were on 16.5% of the farms, which had greater than 50 lambs. About 54% of the lambs were born in January and February. Spring markets and confinement rearing were popular, as only 45.7% of the total lambs grazed summer pasture. Most producers (81.5%) treated their stock sheep (and lambs) for nematodiasis 2 to 4 times per year (mean, 3.3), generally before lambing, before pasturing, midsummer, and/or before breeding. Only 27.5% of the producers indicated distinct drenching management for grazing lambs. There was little use of preventive control, such as spring prophylaxis (0.5%) or dosing in midsummer and moving animals to safe pasture (2.9%). More than one anthelmintic class was used on 59.6% of the farms, with a mean of 1.88 anthelmintics per farm. Though 53.7% of the producers had a policy of alternating anthelmintic classes within a year, only 11.6% alternated anthelmintics annually. Levamisole and thiabendazole were the anthelmintics most frequently used by 81.8% and 61.6% of producers, respectively. However, 26.5% and 16.2% of the farms used fenbendazole and phenothiazine, respectively. The presence of gastrointestinal nematode resistance to anthelmintics was suggested, because 35.4% of the producers had discontinued using at least one anthelmintic that they considered to be ineffective. The anthelmintic that was most frequently discontinued was thiabendazole.(ABSTRACT TRUNCATED AT 250 WORDS)