Horse News & Views - February 2003

Ministry of Agriculture, Food and Rural Affairs

Ontario Association of Equine Practitioners

• John Madigan and his co-researchers from the University of California have provided a new piece to the puzzle of Potomac Horse Fever (PHF). Ehrlichia risticii, the agent of Potomac Horse Fever, is maintained in nature in a complex aquatic ecosystem. Transmission to horses can occur through accidental ingestion of insects such as caddisflies containing infected metacercariae (the intermediary form of trematode parasites). Immature and adult forms of caddisflies, mayflies, damselflies, dragonflies, and stoneflies were found to contain infected metacercariae. (Equine Vet J 2000 Jul;32(4):273-4, J Med Entomol 2000 Jul;37(4):619-625.) Further research will need to determine if PHF is seen in years when these insects are at the peak of their life cycle; if changes to grazing management may have an effect; and if the infected flies remain infective in stored feed.

• Horse owners are often surprised and disgusted when the bottom row of hay bales in their single-storey barns becomes moldy. Moisture from the ground will move upwards, even through concrete floors. Horse owners have used skids and plastic on the floor with disappointing results. To prevent this substantial loss, place plastic vapour barrier on the ground prior to laying the concrete floors. In addition, place one foot of shavings over the concrete prior to storing the bales on the floor. This will prevent hay wastage and the shavings will be used up as the hay is fed.