Seasonal output of gastrointestinal nematode eggs and lungworm larvae in farmed wapiti and red deer of New Zealand.

Gastrointestinal nematode parasites and lungworm are significant animal health issues for farmed wapiti and red deer (Cervus elaphus). Chronic infection with gastrointestinal nematodes, coupled with sporadic, often pathogenic, outbreaks of the lungworm Dictyocaulus eckerti in young deer has resulted in many farmers relying heavily on anthelmintic treatments. An improved understanding of the epidemiology of the parasites infecting farmed deer, including the sources and seasonality of pasture contamination on the farm, is essential to the development of more integrated and sustainable control programs. The numbers of strongyle nematode eggs and lungworm larvae shed by different stock classes (red and/ or wapiti mixed-age stags, mixed-age red hinds, rising 2-year-old red stags and mix-sex rising 1-year olds) were monitored monthly, across six farms located in different regions of New Zealand, from January 2018 to early 2020. Every month, 10 fresh on-pasture faecal samples were collected from each stock class and couriered overnight to the laboratory. Baermann apparatus to recover lungworm 1st-stage larvae were set up immediately on sample arrival. Faecal samples for nematode faecal egg count were stored at 4 °C until the number of strongyle eggs were counted by mini-FLOTAC. Additional information, including stocking density, grazing systems, and anthelmintic treatments, were also noted every collection month. Results indicate a relatively consistent proportion of animals within each stock class shedding low numbers of both gastrointestinal nematode eggs (about 75 %) and lungworm larvae (about 50 %) all year round. There was little apparent seasonality and few differences between farms (location). Further, the average number of eggs/larvae shed was also relatively constant across seasons and locations, within each stock class. Interestingly, there was little correlation between lungworm larval counts and egg counts suggesting that the same animals were not consistently shedding both parasites. The data indicate that in the presence of regular anthelmintic treatments to young deer (< 1 year old), the adult stock groups constitute a potentially significant source of pasture contamination, and hence future infection. However, these data do not incorporate the seasonal effects of weather on egg/larval development, nor the number of animals of each stock class on the farms. Incorporation of these variables will be necessary to identify the sources and timing of subsequent infection. This work is currently underway.