A rare botulism outbreak has killed 23 horses at Whistlin’ Willow Farm in Gorham, Maine, Portland’s Press Herald reports.

No mistreatment has been reported. Some sickened horses recovered, while at least another 40 horses at the farm never became sick.

State health officials believe the toxin developed in bales of silage — feed grass packaged while still moist.

The illnesses occurred between April 7 and 17.

The state veterinarian told the Press Herald that there is little veterinarians can do for horses once they exhibit symptoms of botulism poisoning. The toxin can kill horses within hours of ingestion.

State health officials advise against feeding animals moldy hay.

  • S Ostrowski

    Very distressing to learn of this large outbreak of equine botulism in Maine. A similarly large outbreak occurred in Southern California in 1989. (Kinde H, et al. 1991. Clostridium botulinum type-C intoxication associated with consumption of processed alfalfa hay cubes in horses. JAVMA 199:742-46.)
    Unfortunately, Clostridium botulinum is ubiquitous in soil throughout North America. Wet and spoiled forage (hay, silage, even wilted grass clippings) provide an optimal environment for it to grow and produce botulism neurotoxin (BoNT). Horses appear to be the species most sensitive to BoNT — at least >1000 times more sensitive than the mice used for the classic diagnostic test (the “Mouse BioAssay” or MBA), which makes this a relatively insensitive diagnostic assay for the disease in horses. Clinical signs and prognosis are dose dependent. The mortality rate for adult horses affected by botulism varies by serotype, but recent review articles report 85% – 95% mortality rates; very few survive once they become unable to eat, drink, or stand. For multiple technical reasons, a rapid (point of care)test has yet to be developed. Equine botulism remains a “diagnosis of exclusion” — in other words, a clinical diagnosis arrived at by systematically ruling out other likely possibilities — which makes it very challenging to initiate specific therapy in a timely manner. An affordable trivalent (serotypes A, B, C) antiserum has recently become available, but needs to be administered very early in the illness (per Whitlock and McAdams — see below)
    Recent peer-reviewed references:
    Johnson AL, McAdams SC, Whitlock RH. Type A botulism in horses in the United States: a review of the past ten years (1998-2008). J Vet Diagn Invest (2010) 22:165-173.
    Ostrowski SR, Kubiski S, Palmero J et al. An outbreak of equine botulism type A associated with feeding grass clippings. J Vet Diagn Invest (May 2012); 24(3):601 – 603.
    Whitlock RH, McAdams SC. (2006) Equine Botulism. Clin Tech Equine Pract 5:37-42.

  • JC

    Don’t believe a word of it. GRASSFED IS BEST! Nothing can ever go wrong with grassfed so these smartypants doctors must be lying. They didn’t say if the horses got vaccine but that is probably what killed them.

  • JP

    On the contrary, the vaccine available for horse’s is known to be very safe and effective against type B botulism when administered properly.

  • DSmith

    JC I respect your opinion. But things can go wrong with grassfed horses. As the Doctors said it is in the soil all over the US and Canada. There was an outbreak in Florida in 2008 that kill 114 horses on one farm.
    So you have your facts straight on the vaccine:
    BotVax B is extremely safe. It has been on the market since 1987 sold by the Neogen Corporation exclusively to Veterinarians. It is so safe that infact that in the First Gulf War this vaccine was on backorder to Veterinarians because it was being used to vaccinate our US Troops serving in the Persian Gulf, Iraq, and Kuwait.
    In the 25 years this vaccine has been on the market there have been no adverse events reported. Also there has never been a case of Botulism occur in a properly vaccinated horse.
    If you would like more info please check out http://www.neogen.com and click on the informneogen email link and request information on BotVax B or call (800)525-2022
    The doctors who commented first are actually the worlds formost experts in Equine Botulism.