28 February 2012

4 minute read

Parasite control in cattle

Cattle studies were conducted in Belgium, Germany, Sweden and the UK as part of an EU wide PARASOL project. Field surveys were conducted in calves on > 900 farms using a serum pepsinogen assay and adult cows on > 3700 farms using a Ostertagia antibody ELISA applied to bulk-tank milk. Several pasture management practices were negatively associated with the observed levels of exposure and could be proposed as non chemotherapeutic control measures. Mid-season liveweight gains may be a suitable parameter for selective treatments in first-season grazing calves. The key message to emerge from PARASOL is that TST approaches are effective and economically competitive whilst reducing the rate of development of anthelmintic resistance but need to be coupled with routine monitoring of anthelmintic efficacy.

However, the challenge of getting the ruminant industry to implement this approach in order to conserve efficacy in all anthelmintics remains a formidable one (Vercruysse et al 2010).

Further results from the EU-funded PARASOL project work on cattle was published. Two approaches optimising anthelmintic treatments in cattle were studied; Targeted Treatments (TT)n whole-group treatments optimised on the basis of a marker of infection e.g. faecal egg count (FEC), and Targeted Selected Treatment (TST) - treatments given to individuals that will most benefit from treatment. A number of indicators for TT and TST were assessed to define appropriate regional, parasitological and production-system specific indicators for treatment. These included pepsinogen levels and Ostertagia bulk milk tank ELISA in cattle.

In cattle, bulk milk tank ELISA and pepsinogen assays could be used to determine the levels of exposure and hence optimise TT. The TST approach clearly selected less heavily for the development of resistance in comparison to routine monthly treatments. Further research is required to optimise markers for TT and TST but it is also crucial to encourage producers/advisors to adapt these refugia-based strategies to maintain drug susceptible parasites in order to provide sustainable control (Kenyon and Jackson 2010).

Infections with gastrointestinal roundworms are an important cause of production losses in sheep and cattle. Worm control is a vital part of health and production management in sheep flocks and cattle herds in the UK and good control is highly dependent on effective anthelmintics. Unfortunately, a direct and unavoidable consequence of using anthelmintics to control worm populations is the selection for individuals that are resistant to the chemicals used. Whilst there is some evidence of emerging resistance in roundworms of cattle, it appears to still be at a very low level in the UK.

However, the potential presence of such AR in cattle worms has been seen as a timely warning, which if ignored, could lead to a not dissimilar AR situation to that seen in sheep, and in other cattle areas of the world. Reports of AR in UK cattle nematodes have been limited to a small number of anecdotal reports of treatment failure with some macrocyclic lactone (ML) products, especially those formulated as pour-on preparations. Where these have occurred they have invariably involved the 'doselimiting' species Cooperia oncophora. As a consequence of these observations, guidelines for sustainable worm control strategies for cattle "COWS" (control of worms sustainably) have been produced similar to SCOPS guidelines for sheep, for launch in May 2010 (Taylor 2010).

Immunity in cattle to O.ostertagi

A study was published which aimed to estimate and discuss the genetic variation, heritability, and effects of nongenetic factors on the ability of Holstein-Friesian cows to produce an immune response by producing IgG antibodies to Ostertagia ostertagi.

The ability to produce O. ostertagi antibodies as measured by ODR had a heritability of 0.13 +/- 0.12, and both season of sample and herd had a significant effect on total IgG levels. This study ascertained that genetic variation is present in the ability of dairy cows to mount an immune response to the parasite O. ostertagi.

Inasmuch as evidence exists that IgG is linked to protective immunity against the parasite via a reduction in its reproductive ability, this trait may be of potential interest to genetic selection programs as an aid to reduce the effect of O. ostertagi in dairy herds. (Hayhurst et al., 2010)