Quantitative estimation of the level of exposure to gastrointestinal nematode infection in first-year calves.

In two experiments groups of calves were exposed to different levels and patterns of infection with Ostertagia spp. and Cooperia spp. The experimental design simulated the stereotypic pattern of herbage infestation, including a normal or a delayed midsummer increase, under conditions of set-stocking. The purpose of the experiments was to investigate the accuracy of egg counts, pepsinogen and gastrin values and antibody titres as estimators of the level of exposure to infection. Faecal egg counts significantly reflected levels of exposure during the first half of the simulated grazing season. Antibody titres and pepsinogen values reflected levels of exposure best during August and September, partly depending on the pattern and range of levels of exposure. Antibody titres against Cooperia spp. were particularly useful when levels of exposure to gastrointestinal nematode infection were low. Gastrin values were elevated only at high levels of exposure, which caused large weight gain reductions, in the later part of the simulated first grazing season. It is suggested that antibody titres and pepsinogen values can be used for prognostic diagnosis, indicating whether or not control measures should be taken. Both estimators of infection correlated significantly with the realised weight gain at the end of the simulated grazing season. Egg counts in the second month after the initial infection (turnout) also may be of significant value to support decisions concerning control measures. Comparisons with data from field trials and experiments conducted by others under various conditions suggested that the conclusions of the present experiments are also valid under field conditions. Furthermore, the results supported the conclusions drawn from previous field work, that levels of exposure are often very low on commercial farms in the Netherlands.