A study on some aspects of the pathogenicity, diagnosis and control of gastrointestinal nematodes in deer : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Animal Science at Massey University, Palmerston North, New Zealand

Abstract

The most important parasites in farmed red deer are Dictyocaulus eckerti and gastrointestinal nematodes (GIN). The overall aim of these studies was to develop an understanding about GIN parasites in red deer, including their pathogenicity, diagnosis, control and the risk of cross-infection with cattle/sheep. To understand the pathogenicity of GIN, young deer were trickle infected with a mixed culture of deerorigin infective larvae (L3). The infection comprised 40% Ostertagia-type and 53% Oesophagostomum spp. L3. As a result of the high proportion of Oesophagostomum spp. L3, the animals were clinically affected with large intestinal lesions and it was not possible to investigate the effect of Ostertagia-type parasites. Oesophagostomum sikae was recognised in New Zealand for the first time in this study. A national survey of the prevalence of different GIN in deer utilised PCR-based methodology. From each of 59 deer farms around New Zealand faeces from an average of 19 deer/farm were cultured and 24 infective larvae were randomly selected and identified. The order of prevalence from high to low was Oesophagostomum. venulosum > Spiculopteragia asymmetrica > S. spiculoptera > Ostertagia leptospicularis. This illustrated the importance of abomasal nematodes in the subfamily Ostertaginae. A study was conducted to determine the ability of sheep GIN to establish in deer. The highest establishment rates were Haemonchus contortus (10.5%), Trichostrongylus axei (12.2%) and O. venulosum (5.8%). However, these were all lower than in sheep. The effectiveness of crossgrazing system between deer and sheep (DS) or cattle (DC) compared to deer grazing alone (DD) was undertaken as a replicated study at two locations over two years. The key outcomes were that DC needed fewer anthelmintic treatments and still had higher live-weight than other groups. The DD group received more treatments and still had highest nematode counts for Ostertagia-type nematodes and Dictyocaulus. The DS group received a similar number of treatments to DD and had the highest burdens of T. axei. Cross-grazing offers advantages which varied between DC and DS with regards the level of control of GIN, however, both were effective in controlling lungworm infection. Deer in all groups still required anthelmintic treatment to maintain growth rates