GASTROINTESTINAL NEMATODE INFECTIONS OF FIRST-SEASON GRAZING CALVES IN BELGIUM - GENERAL PATTERNS AND THE EFFECT OF CHEMOPROPHYLAXIS

Comparative analyses of the patterns of gastrointestinal nematode infe ctions of first-grazing season cattle in Belgium are presented. The an alysis involves 17 studies covering a 10 year period on 13 different f arms in Flanders, Belgium. In all studies the calves were divided into an untreated control group, and one or two groups treated with chemop rophylactic systems. Two general infection levels emerged-'sub-clinica l' (14 studies) and 'clinical' (three studies). The 'sub-clinical' inf ections were characterised by no clinical signs of parasitic gastroent eritis in the untreated control groups. Mean faecal egg counts remaine d low (less than 200), maximum pepsinogen levels only reached about 35 00 mU tyrosine, and very small reductions in overall daily weight gain were observed compared with calves given chemoprophylaxis (less than 40 g day(-1)). Based on these results, on these 'sub-clinical' farms, chemoprophylaxis may not have been needed. In contrast, multiple salva ge treatments of the control calf groups were required in the 'clinica l' infections. Even with these salvage treatments mean faecal egg coun ts were high (more than 300), maximum pepsinogen levels were over 5500 mU tyrosine and there was a very large reduction in overall daily wei ght gain (more than 300 g day(-1)). However, it was not possible to pr edict either at turnout, or during the first month afterwards whether an infection on a particular farm would develop into a 'clinical' infe station. With the present data this prediction was possible from 8 wee ks (Day 56) onwards, based on faecal egg counts and pasture larval con tamination. It was also possible to predict using serum pepsinogen lev els on Day 84. Therefore, one possible strategy for the effective cont rol of gastrointestinal nematode infections of calves in temperate reg ions would be to evaluate faecal egg counts 2 months after turnout, an d then only start treatment (i.e. metaphylaxis) if required.