Comparative susceptibility of Pyrenean and Brown Swiss calves to gastrointestinal nematodes in subclinical naturally acquired infections.

The susceptibility of two common breeds of cattle in the Pyrenees, Brown Swiss and Pyrenean breed, to parasitism by gastrointestinal nematodes was studied. Twenty-two female calves (13 Brown Swiss and 9 Pyrenean), 3 months old with a mean weight of 112.8 +/- 18.33 and 103.3 +/- 17.11 kg respectively at the start of the study, were used. The calves began their first grazing season grazing with 200 cattle following the traditional grazing system for mountainous areas: Stabling during winter (December-April), grazing on harvesting meadows at an elevation of 900 m in the spring (May-June) and autumn (October-November), and grazing areas between 1200-2100 m during the summer (July-September). Faeces, blood samples and calves growth rate were taken at 2-week intervals throughout the grazing season. Faecal egg counts of gastrointestinal nematodes, level of serum pepsinogen, total serum protein and blood parameters were measured. The worm egg counts and Cooperia sp. counts were significantly smaller in the calves of Pyrenean breed than in Brown Swiss throughout the experiment. Numbers of eggs of the other genera of parasites found were smaller in the calves of Pyrenean breed than in calves of Brown Swiss breed, but no statistical differences were found. Blood was compared during two periods: the prepatent and patent periods. During the first period, no differences were found between the breeds for any parameter studied. However, during the patent period, Pyrenean animals had significantly greater numbers of erythrocytes, haemoglobin values and packed cell volume (PCV) values, and smaller numbers of eosinophils than animals of the Brown Swiss breed. No differences were found in the level of serum pepsinogen, total serum protein and live weight gains between the two breeds.