Search

As it has been 30 years since a new anthelmintic class was released, it is appropriate to review management practices aimed at slowing the development of anthelmintic resistance to all drug classes. Recommendations to delay anthelmintic resistance and provide “refugia” are reviewed and a simulation model used to find optimum treatment strategies that maintain nematode control. Simulated Australian conditions indicated that a common successful low-risk treatment program was a rapid rotation between a “triple-combination” product (benzimidazole + levamisole + abamectin) and a new high-efficacy drug (monepantel). Where Haemonchus contortus was a threat, moxidectin was required at critical times because of its persistent activity against this parasite. Leaving up to 4% of adult sheep untreated provided sufficient “refugia” for non-selected worms to reduce the risk of selecting for anthelmintic resistance without compromising nematode control. For a new anthelmintic, efficacy estimated by faecal egg count reduction (FECR) is likely to be at or close to 100%, however using current methods the 95% confidence limits (CL) for 100% are incorrectly determined as 100%. The fewer eggs counted pre-treatment, the more likely an estimate of 100% will occur, particularly if the true efficacy is >90%. A novel way to determine the lower-CL (LCL) for 100% efficacy is to reframe FECR as a binomial proportion, i.e. define: n and x as the total number of eggs counted (rather than eggs per gram of faeces) for all pre-treatment and post-treatment animals, respectively; p the proportion of resistant eggs is p = x/n and percent efficacy is 100*(1-p) (assuming equal treatment group sizes and detection levels, pre- and post-treatment). The LCL is approximated from the cumulative inverse beta distribution by: 95%LCL = 100*(1-(BETAINV(0.975,x + 1,n-x + 1))). This method is simpler than the current method, independent of the number of animals tested, and demonstrates that for 100% efficacy at leas

As it has been 30 years since a new anthelmintic class was released, it is appropriate to review management practices aimed at slowing the development of anthelmintic resistance to all drug classes. Recommendations to delay anthelmintic resistance and provide “refugia” are reviewed and a simulation model used to find optimum treatment strategies that maintain nematode control. Simulated Australian conditions indicated that a common successful low-risk treatment program was a rapid rotation between a “triple-combination” product (benzimidazole + levamisole + abamectin) and a new high-efficacy drug (monepantel). Where Haemonchus contortus was a threat, moxidectin was required at critical times because of its persistent activity against this parasite. Leaving up to 4% of adult sheep untreated provided sufficient “refugia” for non-selected worms to reduce the risk of selecting for anthelmintic resistance without compromising nematode control. For a new anthelmintic, efficacy estimated by faecal egg count reduction (FECR) is likely to be at or close to 100%, however using current methods the 95% confidence limits (CL) for 100% are incorrectly determined as 100%. The fewer eggs counted pre-treatment, the more likely an estimate of 100% will occur, particularly if the true efficacy is >90%. A novel way to determine the lower-CL (LCL) for 100% efficacy is to reframe FECR as a binomial proportion, i.e. define: n and x as the total number of eggs counted (rather than eggs per gram of faeces) for all pre-treatment and post-treatment animals, respectively; p the proportion of resistant eggs is p = x/n and percent efficacy is 100*(1-p) (assuming equal treatment group sizes and detection levels, pre- and post-treatment). The LCL is approximated from the cumulative inverse beta distribution by: 95%LCL = 100*(1-(BETAINV(0.975,x + 1,n-x + 1))). This method is simpler than the current method, independent of the number of animals tested, and demonstrates that for 100% efficacy at leas

Diarrhoea (scouring) and subsequent faecal soiling of fleece are important economic and welfare issues for the sheep industry. Nematode worm infections are commonly implicated as a cause of scouring. This study aimed to investigate the extent of strongyle parasite infections, and identify any association with faecal worm egg count (WEC) and scouring in sheep from winter rainfall environments in Western Australia consigned to an abattoir. Faeces were collected from sheep with evidence of scouring and normal sheep (firm faecal pellets and no evidence of fresh diarrhoea on breech). A total of 4430 sheep from 113 lines of lambs (<12 months old), 10 lines of yearlings (12-24 months old) and 235 lines of adult sheep (>24 months old) were sampled between September and January. Mean WEC in lamb lines was 1525 eggs per gram (epg) of faeces with mean WEC >1000 epg in 42% of lines and >2000 in 22% of lines. Mean WEC in adult lines was 486 epg, with 13% lines having mean WEC >1000 epg. There was a trend (P = 0.099) to higher WEC in scouring lambs (2289 epg) compared with normal lambs (1523 epg). The scouring adult sheep had lower WEC (417 epg) compared with normal adults (482 epg, P = 0.021). The findings suggest that large strongyle infections were common in lambs consigned for slaughter. The low WEC in scouring adult sheep was consistent with the suggestion that a hypersensitivity to ingested nematode larvae, rather than large worm burdens, may be responsible for scouring in mature sheep.

Diarrhoea (scouring) and subsequent faecal soiling of fleece are important economic and welfare issues for the sheep industry. Nematode worm infections are commonly implicated as a cause of scouring. This study aimed to investigate the extent of strongyle parasite infections, and identify any association with faecal worm egg count (WEC) and scouring in sheep from winter rainfall environments in Western Australia consigned to an abattoir. Faeces were collected from sheep with evidence of scouring and normal sheep (firm faecal pellets and no evidence of fresh diarrhoea on breech). A total of 4430 sheep from 113 lines of lambs (<12 months old), 10 lines of yearlings (12-24 months old) and 235 lines of adult sheep (>24 months old) were sampled between September and January. Mean WEC in lamb lines was 1525 eggs per gram (epg) of faeces with mean WEC >1000 epg in 42% of lines and >2000 in 22% of lines. Mean WEC in adult lines was 486 epg, with 13% lines having mean WEC >1000 epg. There was a trend (P = 0.099) to higher WEC in scouring lambs (2289 epg) compared with normal lambs (1523 epg). The scouring adult sheep had lower WEC (417 epg) compared with normal adults (482 epg, P = 0.021). The findings suggest that large strongyle infections were common in lambs consigned for slaughter. The low WEC in scouring adult sheep was consistent with the suggestion that a hypersensitivity to ingested nematode larvae, rather than large worm burdens, may be responsible for scouring in mature sheep.

Surveys to assess the use of agricultural practices provide "point-in-time" snapshots of what farmers do on their farms. The results can then be compared across regions or over time. Often, comparisons over time allow an assessment to be made about the efficacy of extension campaigns to change such practices. Gastro-intestinal nematodiasis is a serious production-limiting disease affecting Australian sheep and is further complicated by the widespread occurrence of anthelmintic resistance (1). Awareness of anthelmintic resistance has driven extension efforts to modify the worm control practices employed by farmers. Surveys in the 1980's in Western Australia, estimated worm control practices and showed high levels of benzimidazole and levamisole resistance (3, 4). These findings initiated the "CRACK" campaign, which aimed to limit anthelmintic resistance. With the rising prevalence of ivermectin resistance detected in the 1990's, an extension campaign to modify summer drenching practices was commenced early in 2001-2002. This paper compares five surveys of worm control practices conducted between 1981 and 2002 and discusses the changes against the extension campaigns waged.

Diarrhoea (scouring) is an important issue for the sheep meat industry. Scouring is a major risk factor for fleece soiling and consequential carcase contamination with microbes that cause meat spoilage and potential dangers for humans (2). There is little information on the causes of scouring in sheep at slaughter. Strongyle worm infections are commonly implicated in scouring and reduced production, yet there is no published data quantifying strongyle infections in scouring and normal sheep at abattoirs. In addition, Giardia and Cryptosporidium have been associated with scouring in ruminants, but little is known about the prevalence, genotypes present or the effect on production in sheep populations. This study carried out at an abattoir in Western Australia (WA), aimed to investigate the extent of strongyle, Giardia and Cryptosporidium infections and any association with scouring in sheep.

Although diarrhoea and faecal soiling of fleece are major problems for the sheep meat and wool industries, there is little information on the nutritional factors that determine faecal consistency in sheep. Research in monogastric species has shown that the soluble non-starch polysaccharide (sNSP) content of the diet is a major determinant of faecal consistency and susceptibility of animals to enteric diseases (2, 3), but there have been no studies on the role of sNSP in sheep. sNSP have profound effects on the physio-chemical conditions of the gut lumen by increasing viscosity of digesta and affecting microbial fermentation in the large intestine (2). Carboxymethylcellulose (CMC) is a non-fermentable viscous-forming agent that has been used in pig diets to study the effect of sNSP of increasing digesta viscosity, independently of potential effects on fermentation (2). This study aimed to investigate if CMC could be used as a model for studying the effect of increasing digesta viscosity in sheep and whether dietary CMC supplementation would have any detrimental effects on faecal consistency.