Survey of parasite control on sheep farms in south-west England

Autor: Clare Dixon, Gerald C. Coles, E F Dale, C H J Barton
Rok vydání: 2006
Předmět:
Zdroj: Veterinary Record. 158:55-57
ISSN: 0042-4900
DOI: 10.1136/vr.158.2.55
Popis: THE control of parasites is essential for the maintenance of sheep welfare and productivity, and relies to a large extent on the use of chemicals. There is little information in the public domain on the chemicals used, the control strategies adopted and farmers’ perception of the extent of drug resistance in the parasites of sheep. A postal survey of worming practises and anthelmintic resistance concluded that most sheep farmers are not adopting strategies designed to reduce the development of resistance (Coles 1997), and a survey in Scotland highlighted that practises to slow the development of resistance have not been adopted (Sargison and Scott 2003). A comparison of Veterinary Investigation Diagnosis Analysis (VIDA) data from 1996 to 2003 on cases of disease diagnosis (Veterinary Laboratories Agency [VLA] 2005) with the numbers of outbreaks of sheep scab from 1973 to 1992 (French and others 1999) shows clearly that sheep scab has become more widespread in the UK, but the extent of the problem is not known. This short communication describes a survey of sheep farms in south-west England on their parasite control strategies. Three hundred farmers in south-west England, listed in the ‘Yellow Pages’, were contacted by letter and then by telephone; previously, letters sent to 1000 members of the National Sheep Association in the same area of the country had produced few responses. Most of the 300 farmers did not have sheep flocks, but 90 with sheep agreed to complete the questionnaire, which comprised 14 questions on management strategies, 14 questions about anthelmintic use and perceived problems with anthelmintics, six about sheep scab and lice, three about blowfly, six about coccidia, five about liver fluke and three about tapeworms, and which included questions on the actions taken to avoid the introduction of parasitic infections. Data was entered on Epi Info (Centers for Disease Control) for analysis. The respondents’ flocks ranged in size from 300 to 1400 ewes, and the altitude of the farms from sea level to 350 m above sea level, with many farms covering a range of altitudes. Eighty-four per cent of the farmers housed their ewes for periods of one week to three months at lambing time; 16 per cent did not house their ewes. The mean stocking density was 2·5 ewes per acre (6·3 ewes per hectare), with a range of less than one to seven ewes per acre. Sheep and cattle were kept by 76 per cent of the farmers, and 82 per cent of these rotated sheep and cattle on the same pastures. Although 29 per cent of the farmers stated they ran closed flocks, the majority of these brought in rams, so the flocks were not truly closed. Forty-eight per cent of the farmers who brought in new stock stated that they always isolated the new animals; the isolation period varied from one week to three months (mean 2·3 weeks). Seventeen per cent sometimes isolated new animals, while 35 per cent reported that they never isolated new animals. Forty per cent used an avermectin/ milbemycin on new stock, 13 per cent used levamisole or levamisole plus triclabendazole, 8 per cent used a benzimidazole and 3 per cent used mebendazole plus closantel, while 36 per cent did not treat incoming sheep with anthelmintics. Nine farmers (10 per cent) treated introduced sheep with a pouron ectoparasiticide before mixing them with the existing flock. Of seven farmers who hired rams, six had them treated for ectoparasites before their arrival on the farm. All the farmers treated for nematodes, and 88 per cent planned their own control strategies based on a variety of sources, chiefly the farming press (37 per cent), agricultural merchants (29 per cent) and their veterinary surgeons (27 per cent). Advertisements in the farming press and information from DEFRA apparently had little impact. Macrocyclic lactone products were the most frequently used in the previous three years (Fig 1). The farmers’ reason for their choice of anthelmintic was based primarily on past experience (56 per cent) followed by cost (22 per cent), with reliability, their veterinary surgeon’s advice and convenience being less influential. Rams were dosed at the same time as ewes by 86 per cent of the farmers, and 8 per cent of the farmers did not treat their rams. Most of the farmers (58 per cent) dosed lambs frequently until they were sold. Only one farmer ran an organic flock and did not use prophylactic treatments. The numbers of treatments per year given to lambs and ewes is shown in Fig 2: the mean frequency for lambs was three treatments, with a maximum of five, and for ewes the mean was 2·3 treatments, with a maximum of four treatments. Nine per cent of farmers treated their lambs ‘as necessary’. Fifty-four per cent changed the anthelmintic they used each year, while 35 per cent changed less often and 11 per cent changed more often. Some of the changes were within anthelmintic families rather than between families. Sixty per cent of the respondents were concerned about anthelmintic resistance and worm control in the future; 32 per cent stated that they had checked for resistance using faecal egg counts and 28 per cent had had anthelmintic failures, which had been dominated by benzimidazole resistance. Sheep were turned out on to ‘clean’ pasture by 86 per cent of the farmers. The husbandry practices on the farms reporting anthelmintic failures suggested that relatively high treatment frequencies of ewes and lambs, combined with treatment followed by a move to ‘clean’ pasture, were common features on those farms (Table 1). Twenty-four per cent of the farmers reported previous problems with liver fluke and 9 per cent stated that their stock was currently affected, but 51 per cent were using prophylactic treatments. Of the farms using fasciolicides, 17 per cent had used triclabendazole, 37 per cent had used triclabendazole plus levamisole, 22 per cent had used oxyclozanide plus levamisole, 11 per cent had used mebendazole plus closantel and 11 per cent had used albendazole, and one farmer reported using oxfendazole. Twenty-eight per cent said they had noticed tapeworm segments in the faeces of the lambs, but none considered this a problem. Thirty-one per cent of the farmers stated that they had had coccidiosis in their flocks, and in 93 per cent of these cases it N um be r of fa rm er s 60
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