Effect of naturally occurring nematode infections in the first and second grazing season on the growth performance of second-year cattle.

Antibody titres against Ostertagia spp., Cooperia spp. and Dictyocaulus viviparus as well as pepsinogen values, reflecting exposure to nematode infection, differed significantly among herds of second-year cattle on 87 farms. Faecal examinations revealed that gastrointestinal nematode infections were present in all herds. Similar results were found in yearling-herds on the same farms a year earlier. Liveweight of yearlings per herd deviated from -64.7 kg to +94.4 kg from an age-adjusted population mean after the second grazing season. This mean herd weight deviation was significantly related negatively to antibody titre against Ostertagia spp. (linear regression, P less than 0.05; segmented curvilinear regression, P less than 0.01) and to antibody titre against Cooperia spp. (segmented curvilinear regression, P less than 0.05), both measured in the second grazing season. Antibody titre against Ostertagia spp. measured in the first grazing season, when yearlings were calves, was significantly correlated positively to age-adjusted body weights at the end of the second grazing season. The results suggested that immunity built up during the first year had a positive effect on growth performance in the second year, but that on average the acquired immunity was insufficient to prevent reduced weight gains in the second grazing season.