In vitro effect of burned pasture soil on eggs and free-living larvae of ruminant gastrointestinal nematodes

Abstract

Gastrointestinal nematodes are the most expensive agent of disease currently facing the livestock production industry. Spending the beginning of their life cycle as eggs and free-living larvae, nematodes are vulnerable to a multitude of external environmental factors. Fire is a naturally occurring force of nature that has both destructive and reconstructive effects on soil characteristics which nematode stages rely on for survival. The aim of this project was to evaluate in vitro the effect of burned pasture soil (200 °C and 500 °C) on the free-living stages of ruminant nematodes. We tested the effect of burned soil on the ability of eggs to hatch and produce infective larvae, and then tested survival of infective larvae within burned soil. Adding burned soil (500 °C) to larval cultures improved larval yield compared to larval cultures containing raw soil or soil burned at a lower heat (200 °C), and raw soil improved longer term survival of infective larvae. We were able to recover significantly more larvae from samples with low soil content either as raw or soil burned at 200 °C, when compared with samples with soil burned at 500 °C. This study has shown that the survival of gastrointestinal nematodes at the L3 stage is negatively impacted by the addition of soil burned at 500 °C. Although this temperature is closest to that of a medium intensity wildfire, which is a typically destructive process in agriculture, it reduces the number of infective GIN larvae available for animals to ingest. These experiments enable us to address in vitro if post-fire soil conditions alter the number of infective larvae available on pasture, and thus the infectivity of the pasture to livestock.