Brown Besier

Anthelmintics are typically used to control worms and combat their deleterious effects on productivity, but inappropriate use has resulted in widespread resistance of worms to available anthelmintic treatment groups (Sutherland and Scott 2010). Adoption of new management strategies is required to slow the development of anthelmintic resistance. One potential strategy includes leaving a proportion of a flock untreated, which allows non-resistant (susceptible) worms to survive and thus slows the rate at which resistant genes accumulate in the worm population (Kenyon et al. 2009). The most appropriate indicator for selecting sheep that are to remain untreated is not clear. It is widely believed that sheep with a high body condition score (BCS) are better able to cope with worms (i.e., they have higher worm resilience) than sheep with low BCS, but little field research has been undertaken to verify this. Worm resilience is the ability to maintain an acceptable level of production despite a worm burden (Bisset et al. 2001). Figure 1 demonstrates a hypothetical relationship between BCS and worm egg counts (WECs) for worm resilient and non-resilient sheep.

Scouring (diarrhoea) in sheep is an important issue for the sheep meat industry. Soiled fleeces are a significant source of carcase contamination with microbes that include human pathogens and microorganisms that cause meat spoilage (Newton et al, 1978) and scouring is the major risk factor for fleece soiling (French and Morgan. 1996). However, there is little information regarding the causes of scouring in sheep at slaughter. Strongyle worm infections are a commonly implicated cause of scouring, reduced wool production, poor growth rates and reduced bodyweight with young sheep being particularly susceptible (Besier, 2004). However, there is no published data quantifying strongyle infections or scouring in sheep at abattoirs. This study aimed to investigate the extent of strongyle infections and any association with scouring in sheep at an abattoir in Western Australia.

Nine flocks of sheep with "low worm egg count scouring" in the south west of Western Australia were investigated over a three-year period. There was no significant difference in the faecal worm egg counts of "scouring sheep" (diarrhoea and severe dag) compared to "normal sheep" (pelleted faeces and mild or no dag). Teladorsagia (Ostertagia) circumcincta and Trichostrongylus spp were the strongyles most commonly identified on total worm counts and differentiation of larvae recovered from faeces and pasture. Immature strongyle worms accounted for the largest proportion of total worm counts. Adult worm burdens were small in most sheep. Scouring sheep had significantly higher numbers of early fourth stage larvae. There was no histopathological evidence of bacterial or viral causes of scouring in any of the flocks that could be supported with bacteriology. Two flocks had marginal selenium status. One flock was diagnosed with helminthosis based on increased worm egg counts and high total worm counts. Larval hypersensitivity scouring, nutrition or a combination of these two factors were the most likely causes of scouring in the other eight mobs based on exclusion of other known causes of scouring. Treatment with moxidectin drench and an ivermectin controlled-release capsule did not change faecal moisture of treated sheep compared to untreated sheep three to five weeks after treatment.

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.

Strongyle infections and diarrhoea are major problems for the sheep industry, but the nutritional factors determining faecal consistency and susceptibility to enteric diseases are not well understood. Soluble non-starch polysaccharides (sNSP) have been shown to affect the physico-chemical environment of the gut lumen, by increasing viscosity of digesta and affecting microbial fermentation in the large intestine; however, the role of sNSP in sheep has not been studied. sNSP have been shown to increase parasite establishment in the small intestine of mice (3) and decrease parasite establishment in the large intestine of pigs (2). Carboxymethylcellulose (CMC) is a non-fermentable viscous-forming agent that is used to study the effect of soluble NSP in increasing digesta viscosity independent of potential effects on fermentation (I). The aims of this study were to investigate whether increasing viscosity of digesta using CMC may affect establishment of Trichostrongylus colubriformis and Telodorsagio (Ostenagia) circumcincta in sheep and whether the type of roughage and CMC may affect faecal consistency in sheep with strongyle infections.

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.