Sten-Olof Dimander

Assessing the feasibility of targeted selective treatments for gastrointestinal nematodes in first-season grazing cattle based on mid-season daily weight gains

A retrospective study was carried out to assess the possibility of using daily weight gain in first-season grazing cattle (FSG) as a marker for treatment decisions to prevent parasite-induced losses caused by gastrointestinal (GI) nematodes. This is intended as a proof of concept for using targeted selective treatments (TSTs) in the control of veterinary parasites. Historical data were combined from three independent grazing trials in Sweden, each of which was repeated over 2-3 years, in order to investigate the influences of parasites on the performance of FSG cattle subjected to different levels of parasite control. In general, the different trials and years produced congruent results. There was a good positive linear relationship between daily weight gains (Dwgt) registered around housing and those recorded in the middle of the grazing season (r(2)=0.54) but not between early-season Dwgt and housing Dwgt. The latter observation emphasizes that factors other than nematode infection influence the final weight of the cattle. However, significant differences in Dwgt ( approximately 0.2 kg/day) were also observed depending on the nematode-control level achieved. At selected time points, the mean number of trichostrongylid eggs, serum pepsinogen concentration and Ostertagia antibody levels were significantly higher in animals with poor performance. ROC analyses showed that anthelmintic treatment of animals with a Dwgt of <0.75 kg/day by mid-season had a sensitivity of approximately 70% and a specificity of approximately 50%. It thus seems feasible to base a targeted selective treatment for FSG cattle on Dwgt recorded approximately 4-8 weeks after turn-out, provided that it is accepted that some animals will be dewormed without indication. This now needs to be tested in controlled field trials.

Disintegration of Dung Pats from Cattle Treated with the Ivermectin Anthelmintic Bolus, or the Biocontrol Agent Duddingtonia flagrans

AbstractAn experiment was performed during the grazing seasons of 1998, 1999 and 2000 to study the influence of the antiparasitic drug ivermectin and the nematophagous fungus Duddingtonia flagrans on cattle dung disintegration. The faeces originated from groups of animals that were part of a separate grazing experiment where different control strategies for nematode parasite infections were investigated. Each group consisted of 10 first-season grazing cattle that were either untreated, treated with the ivermectin sustained-release bolus, or fed chlamydospores of D. flagrans. Faeces were collected monthly on 4 occasions and out of pooled faeces from each group, 4 artificial 1 kg dung pats were prepared and deposited on nylon mesh on an enclosed pasture and protected from birds. The position of the new set of pats was repeated throughout the 3 years of the study. Each year, the dung pats were weighed 4, 6, 8 and 10 weeks after deposition and immediately afterwards replaced to their initial positions.Results showed that there was no difference in faecal pat disintegration between groups. However, the time-lag between deposition and complete disintegration of the faeces varied significantly between deposition occasions. Dung pats disappeared within 2 weeks (visual observation) when subjected to heavy rainfall early after deposition, whereas an extended dry period coincided with faeces still remaining 12 months after deposition.Svensk sammanfattningNedbrytning av träck från kalvar behandlade med avmaskningsmedlet ivermektin eller rovsvampen Duddingtonia flagrans. I föreliggande studie undersöktes nedbrytningshastigheten av komockor experimentellt. Under betessäsongerna 1998 till 2000 preparerades träck årligen vid 4 tillfällen från 3 grupper om vardera 10 förstagångsbetande kalvar. Kalvarna var antingen obehandlade, behandlade med en vomkapsel innehållande avmaskningsmedlet ivermektin eller utfodrades med sporer av rovsvampen Duddingtonia flagrans. Fyra konstgjorda komockor tillverkades av en blandning träck från respektive djurgrupp och placerades på nylonnät på en betesyta som hölls fri från betesdjur och skyddade från fågelangrepp. Vägningar utfördes 4, 6, 8 och 10 veckor efter utplacering. Placeringen av komockorna för de olika behandlingarna och de olika deponeringstillfällena upprepades under de 3 åren.Resultaten visade att ihållande regn i samband med, eller kort efter utplacering medförde att synlig träck försvann helt inom 2 veckor (visuell observation). I samband med långvarig torka fanns däremot rester av komockorna kvar upp till 12 månader efter deponering. Nedbrytningshastigheten påverkades dock inte av om träcken kom från kalvar behandlade med ivermektin eller rovsvamp.Studien visar att träcknedbrytningen framförallt påverkades av nederbördsmängd och nederbördsintensitet medan komockornas innehåll av ivermektin eller rovsvamp inte påverkade nedbrytningshastigheten jämfört med mockorna preparerade från obehandlade kalvar. Detta utesluter emellertid inte att ivermektin eller D. flagrans kan inverka negativ på nedbrytningshastigheten av träck, men denna möjliga effekt överskuggades i föreliggande studie av meteorologiska faktorer.

Soil Nematode Populations Beneath Faecal Pats from Grazing Cattle Treated with the Ivermectin Sustained-release Bolus or Fed the Nematophagous Fungus Duddingtonia flagrans to Control Nematode Parasites

The size and composition of the nematode assemblage in soil under faecal pats derived from young cattle treated or untreated with either ivermectin sustained-release boluses, or the nematophagous fungus Duddingtonia flagrans, were studied in each of three years. Soil samples taken 4, 6, 8 and 10 weeks after four deposition dates in 1998 showed significant temporal effects in many taxa and treatment effects in a few genera. In 2000, soil samples taken 10 weeks after deposition in July, August and September showed treatment effects in the plant-associated Tylenchus and Cephalenchus, and the bacterial-feeding Cephalobus 1 and Cephalobus 2 taxa. However, overall it was found that the nematode assemblages were similar below all three types of pat, and the assemblages varied with the season of deposition. D. flagrans, the novel biological control agent being tested against the free-living stages of nematode parasites of cattle, had no detectable impact on the size or the structure of the soil nematode communities under the faecal pats.