Control of gastrointestinal parasites in first- and second-season grazing cattle in Sweden

Gastrointestinal (GI) parasite infections are of major concern for productivity and health of first-season grazing (FSG) cattle in Sweden. Both GI nematodes and the coccidium Eimeria alabamensis overwinter on the pasture, which has major epidemiological implications. Clinical infections are seen as diarrhoea, anorexia and weight loss, while sub-clinical infections induce weight gain penalties that are easily overlooked. This thesis is based on grazing experiments that focus on the control of pasture-borne GI parasites in FSG cattle in Sweden, and the consequences of various levels of infection during their second grazing season (SSG cattle). For 3 consecutive years, FSG cattle were allocated to 4 groups with 10 animals in each, and subjected to either 1) rotational grazing with a 2-paddock system, 2) nutritional supplementation in early season, 3) no treatment (minimum parasite control) and 4) regular treatment with anthelmintics (maximum parasite control). During the first grazing season, animal performance and parasitology were recorded, and pasture infectivity was investigated through tracer animals and pasture larval counts. The same 40 animals were monitored on communal pasturelands during their second grazing season. In addition, the effects of artificial single or concurrent infections with E. alabamensis and GI nematodes were assessed in a separate grazing experiment. Rotational grazing for FSG cattle was successful, and the same aftermath paddock proved parasitologically safe by mid-July for consecutive years. In contrast, severe diarrhoea and weight loss were seen in supplementary-fed and untreated FSG cattle, which may be explained by significant numbers of overwintered GI nematode larvae and E. alabamensis oocysts in the paddocks at spring turn-out. In the study with SSG on communal pasturelands, the weight gain penalties induced in the first grazing season largely remained at the end of the second grazing season in 2 out of 3 years. In addition, the importance of lungworm infections was demonstrated in previously unexposed SSG cattle. The experiment with artificial infections with E. alabamensis and GI nematodes showed no synergy between E. alabamensis and GI nematode infections, whereas dramatic clinical symptoms and production losses from E. alabamensis infections were seen