Observations on the free-living stages of cattle gastrointestinal nematodes.

ABSTRACT

A 4-year study on the free-living stages of cattle gastrointestinal nematodes was conducted to determine (a) the development time from egg to infective larvae (L3) inside the faecal pats, (b) the pasture infectivity levels over time, and (c) the survival of L3 on pasture. Naturally infected calves were allowed to contaminate 16 plots on monthly basis. Weekly monitoring of eggs per gram of faeces (epg) values and faecal cultures from these animals provided data for the contamination patterns and the relative nematode population composition. At the same time, faecal pats were shaped and deposited monthly onto herbage and sampled weekly to determine the development time from egg to L3. Herbage samples were collected fortnightly over a 16-month period after deposition to evaluate the pasture larval infectivity and survival of L3 over time. The development time from egg to L3 was 1-2 weeks in summer, 3-5 weeks in autumn, 4-6 weeks in winter, and 1-4 weeks in spring. The levels of contamination and pasture infectivity showed a clear seasonality during autumn-winter and spring, whilst a high mortality of larvae on pasture occurred in summer. Ostertagia spp., Cooperia spp. and Trichostrongylus spp. were predominant and a survival of L3 on pasture over a 1-year period was recorded in this study.