Two horses at a rescue in Nova Scotia have died as the result of botulism from eating contaminated hay.

CBC reported today that two horses, aged 29 and 12, at Integrity’s Haven Equine Rescue Centre Society in Chester Basin, N.S., died last week, and third horse, eight-year-old Koko, is still battling the effects of the disease.

According to the Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA), botulism “occurs when toxins produced by the bacterium, Clostridium botulinum, enter the horse’s body causing weakness which may progress to paralysis. The botulism bacterium is a spore-forming, anaerobic bacteria (grows in the absence of oxygen) which is found world wide. It is commonly present in soil and in decaying animal carcasses. It occurs less often in decaying plant material. Hay, and especially haylage, can be contaminated with the botulism bacterium during the raking and baling process. The higher moisture levels (in comparison to dry hay), the anaerobic conditions and a pH above 4.5 in some haylage are ideal conditions for the growth of this bacterium.

“When the bacterium grows, it produces one or more toxins. These toxins block the connection between the nerves and muscles. As a result, affected horses often exhibit signs varying from muscle weakness to paralysis.

“Affected horses:

  • usually have muscle tremors
  • may be so weak that they cannot stand up
  • lose control of their tongue so it may hang from their mouth
  • can’t eat and they drool because they can’t swallow
  • may walk stiffly with a short stride or they may be weak and stumble
  • tail may lose its tone

“Eventually they die because their respiratory muscles become paralysed or because they get other health problems from being down. These clinical signs can occur within several hours or up to seven to 10 days post ingestion of the contaminated feed.”

In this case, the rescue centre’s owner, Angela Welburn, said the horses were not fed haylage, and instead contracted the disease from eating dried hay.

While there is a vaccine to protect against botulism, Welburn’s horses had not received it. According to OMAFRA,” an inactivated toxoid is used to vaccinate against botulism. A toxoid is a toxin which has been treated to destroy its toxicity but retains its ability to generate an immune response when injected into an animal. Neogen Biologics, Michigan, USA, manufactures Bot Tox-B (1). It is available in Canada from some suppliers. It protects against Type B only. A three-initial-dose vaccination program is recommended followed by a single annual vaccination.”

If you have concerns, contact your veterinarian for more information, and consider having your hay tested.