Field study on the survival, migration and overwintering of infective larvae of horse strongyles on pasture in central Ukraine.

The research is a field study on how infective larvae of horse strongyles survive, migrate and manage to live through winter, or ‘overwinter’, in pastures in central Ukraine. The study examined the lifecycle of these internal parasites in naturally infected horses and studied their presence in faecal samples at different times of the year, comparing this to control samples.

Methodology

• Researchers placed faecal samples from naturally infected horses onto pasture land between November 2002 and April 2004, excluding winter months.
• Roughly each month, they took samples from these faeces and the surrounding vegetation to measure the quantity of infective, third-stage larvae. The frequency of nematophagous fungi, which the study reveals could impact the survival of the larvae, was also noted.
• In the laboratory, they compared these results to control faecal samples, giving them an understanding of the prevalence and survival rates of these larvae under different conditions.

Results

• In the control samples, the ratio of infective larvae to the initial number of eggs ranged from 54.7% in June to 84.2% in November, depending on the presence of nematophagous fungi growing in the faeces.
• On the actual pasture, the larvae matured to the infective stage over roughly four weeks in the warm season (April-September). In October, a percentage of the eggs didn’t hatch, with no larval development seen in November’s faeces.
• Only a tiny portion of larvae (about 0.03% of their initial number) survived on pasture for a whole year.
• Though the migration of infective larvae from faeces to surrounding vegetation wasn’t intensively observed, the study found that between 71% and 89% of larvae were still present in the original faecal matter four weeks after being deposited on pasture. They noted that this result seemed to correlate with soil moisture levels.
• The faecal samples that were deposited on the pastures in September the previous year had the highest proportion of surviving larvae over winter – up to 42.0%. Some larvae also survived winter in the soil beneath these faecal deposits.

Conclusions

• The research concludes that the pastures in central Ukraine are never completely devoid of infective third-stage larvae of strongyles, suggesting that this parasite could potentially infect horses year-round.
• However, the study also shows that survival rates fluctuate throughout the year, revealing potential windows to target treatments and potentially lower the risk of horses becoming infected.