Gastrointestinal (GI) nematode infection and diagnostic indicators in dairy cows

Abstract

There is a need to identify only those animals with parasite burdens that are likely to benefit from anthelmintic treatment in order to minimise the development of drug resistance in nematodes. Although evidence from Europe and North America suggests that antibody levels to GI nematode infection are inversely linked to production in adult dairy cattle (Charlier et al., 2009 and Sanchez et al., 2004), no such link has been shown, to date, in New Zealand. The objectives of this study were to seek associations between serum or milk antibody levels to GI nematodes and infective larvae availability on pasture, adult parasite burdens and faecal egg count (FEC) expressed as egg per gram (EPG). A group of lactating dairy cows at high stocking density and fed supplements were compared with a low stocking density group (n=30), by monthly monitoring for milk yield, pasture L3 larvae, FEC, milk and serum antibody levels to gastrointestinal (GI) nematodes. Mean EPG was low in both the groups, neither mean EPG nor the proportion of cows showing positive FEC were influenced by stocking density over the whole lactation season. Further, FEC in either group did not correlate with milk yield (production). Immunological analysis has not yet been completed.