The periparturient rise in nematode eggs at lambing is a crucial part of the epidemiology of nematode infections as it allows a large number of infective larvae to be present in the pastures when the lamb is young and most immunologically naïve. With a rapidly rising level of anthelmintic resistance and increasing public concern over drug residues remaining in animal products, it is necessary to achieve more long-term, sustainable nematode control programmes. Some plant products could provide alternatives or adjuncts to conventional control with anthelmintics and ease the selection pressure for anthelmintic resistance. The polyunsaturated fatty acid, docosahexaenoic acid (DHA), which can be produced in high concentrations by some marine algae, has been shown to modify immune response in many species and decrease the production of proinflammatory cytokines (Calder, 2001). This action could reduce inflammation in the gut in response to parasite infestation and reduce the extent of associated hypophagia. The objective of this study was to investigate the long term effects of providing an algal DHA dietary supplement in late pregnancy, on the periparturient rise and the resulting effects on the infection levels and production consequences for their lambs.