The epidemiology of equine strongylosis in southern Queensland. 2. The survival and migration of infective larvae on herbage.

This study investigates the development and longevity of horse nematode larvae on grass. It discovered that more of these harmful parasites survived over longer periods in winter than in summer. The research also noted the distribution and mobility of the larvae, finding that more of them were present lower down than higher up in the grass.

Objective and Method

• The research sought to understand the life cycle and behavior of strongylid nematodes, a harmful parasite affecting horses, by studying its infective larvae. The focus was specifically on how seasonal changes impact their survival rate on herbage and their migration habits.
• Observations and data collection were carried out during different seasons namely; summer, winter, spring and autumn, noting the percentage of survival and duration of survival in each season.
• The study also paid attention to the distribution of larvae within the pasture, noting the heights at which they could be recovered.

Findings

• In summer, only 1% of the larvae were found to survive for 2-3 weeks and of these, 0.2% remained viable for another 2-3 weeks.
• The winter season, however, allowed for a longer survival period, with larvae lasting between 7-11 weeks and over 11 weeks respectively.
• The spring and autumn seasons saw larvae surviving for periods between 3-8 weeks.
• On Rhodes grass (Chloris gayana), it was observed that most of the larvae existed in the lowest layers of the pasture within 10 cm of the soil surface. Very few reached the highest fraction sampled, which was above 40 cm from the soil.
• Periods with less torrential rain saw more larvae being recovered at higher points in the pasture.

Conclusion

• The study concludes that the possibility for beneficial effects of mixed grazing involving horses and cattle might be limited.
• This assertion is based on the observation that cattle tend to consume the upper layers of the pasture initially which results in an increased concentration of infective larvae in the remaining herbage.