Worm burdens can vary greatly between horses, even those living within the same herd. A recent study investigated how faecal egg counts (FECs) relate to parasite infection levels and how variation in egg shedding can influence parasite-control strategies.
What did they do?
The researchers analysed faecal egg count data from horses to determine how egg shedding differed between individuals, whether this variation followed predictable statistical patterns, and how these patterns could inform treatment decisions.
Key Findings:
Parasite burdens were found to be highly over dispersed, meaning a small proportion of horses carry most of the worms. Roughly 20% of horses carry around 80% of the parasite burden. This means that while most horses shed relatively few eggs, a small proportion shed large numbers. This uneven distribution has important implications, as it suggests routine blanket deworming may often be unnecessary.
The study also showed that the average faecal egg count within a herd can help predict infection patterns. When the herd’s mean egg count is high, many horses are likely infected. When the average is moderate, only some horses tend to carry heavy burdens.
Importantly, the link between the average egg count and the differences between individual horses stayed consistent across groups. This suggests the pattern is a natural feature of parasite populations rather than something caused by temporary conditions or local factors.
What does this mean for parasite control?
In practical terms, these findings support more targeted parasite-control strategies. If the average egg count in a herd is high, treating all horses may be appropriate. However, when counts are moderate, selective treatment of higher-risk individuals may be more effective. Treatment decisions could therefore be based on herd averages or risk categories rather than routine blanket dosing.
Overall, this research highlights how understanding patterns in egg shedding can improve parasite management. Targeted selective treatment not only reduces unnecessary drug use but may also help slow the development of anthelmintic resistance, supporting more sustainable parasite-control programmes in horses.
