Botulinum toxin is the neurotoxin protein created when botulism spores grow. The requirements for growth and/or for keeping the toxin from denaturing would seem to be very difficult to create in bale of hay.

There are well documented incidents of botulism in horses who are eating hay, all the references I found were centered around hay in large plastic wrapped bales.

I have been involved in an event where the presumed DX is botulism secondary to ingestion from hay from last year. In this case the hay is second cutting timothy hay (making it 6 plus months old), in rectangular 50 pound (22 kg) bales that are not wrapped, have been barn kept, and when purchased from the vendor where stacked in rows 4 feet wide, by 6 feet (2 meters) high. The bale then spent more then a week on an shelf (chrome platted heavy wire) with good air circulation.

Three pet house rabbits appear to have been effected. with 2 dead and one recovering from a case of descending paralysis. Several tests are underway, but my understanding is that it may be difficult to conclusively show either the botulism in the rabbits, or significant presence of 'botulinum toxin' or 'clostridium botulinum' in the hay (samples from the mangers of effected animals are being tested).

Is it possible to logically conclude that Botulinum toxin could, or could not, be created and/or survive in a bale of hay meeting the above criteria?


If there is an awareness of a plant based neurotoxin that would cause similar symptoms that may be growing in the hay field please offer that in an answer at Gardnening.

  • 2
    $\begingroup$ It's been a long time since I knew the ins and outs of botulinum toxin, but I do seem to recall that it's pretty resilient. Botulism is pretty distinct as far as symptom progression. I'll see if I can do more research and return. $\endgroup$
    – MCM
    Jun 12, 2014 at 12:41
  • $\begingroup$ @MCM, thanks it would be really great if you could shed some light on this. $\endgroup$ Jun 14, 2014 at 12:10

2 Answers 2


Clostridium botulinum toxin is present ubiquitously in soil. As such it is more than plausible that hay bails, which come into contact with soil can and I should expect almost probably will be infected with these bacteria. However it is not the mere presence of the bacteria itself which causes poisoning, it is the toxins they produce when the appropriate conditions are met. These toxins are produced as a consequence of spore formation.

Traditionally in human cases, the presence of toxins has been linked to home canned foods, where there is an anaerobic environment with a ph < 4.5 (http://cid.oxfordjournals.org/content/41/8/1167.full). It is conceivable that such an anaerobic environment exists within a hay bail (even if not wrapped). The following site from the ontario minestry agriculture and food (http://www.omafra.gov.on.ca/english/livestock/horses/facts/info_haylage.htm) suggest that the pH certain methods of hay bailing have pH < 5. This would seemingly confirm hay as potential source for botulinum toxins.

With regards to testing the hay for C. botulinum I would expect there to be a very high chance of finding this, due to soil contamination, however this does not imply this was a definite source for poisoning. A more conclusive test would be for the toxin. So in summary it is logical to suggest that hay could be the toxin source, but this does not mean it was the source.

  • $\begingroup$ This is a very good answers, full of information. I choose to award the bounty to @MCM as that answer more directly addresses the root question about the toxin surviving. Thank you both for your answers. $\endgroup$ Jun 22, 2014 at 10:42

As an addendum to Spinorial's answer, and after some research, the Center for Food Security and Public Health specifically lists hay / grass / decaying vegetable matter as a potential source for C. botulinum growth in their (very informative) Botulism PDF.

All species of Clostridium can produce spores, dormant forms of the organism that are highly resistant to disinfectants, heat and environmental conditions that kill vegetative cells. These spores can survive for many years until favorable conditions allow them to germinate and grow. C. botulinum spores are common in the environment...
... Different strains or groups of C. botulinum may have somewhat different requirements. For instance, the acidity necessary to inhibit C. botulinum type C strains is reported to be pH 5.1 to 5.6, but other organisms can survive a lower pH. Each group also has an optimal, minimal and maximal temperature for growth. For example, some group II organisms may be able to grow in foods at refrigeration temperatures (3-4°C/ 37-39°F), but group I organisms and type C toxin-producing strains are inhibited. Because C. botulinum does not compete well with other microorganisms, growth is more likely to occur if other bacteria and molds have been killed or inhibited. C. botulinum spores can survive cooking and some food- processing conditions that kill vegetative cells, then germinate and grow in the cooked food.

As for your question...

Is it possible to logically conclude that Botulinum toxin could, or could not, be created and/or survive in a bale of hay meeting the above criteria?

Could the toxin survive? Probably. The toxin itself isn't particularly hearty, BUT...

Could the spores survive (and go on to create the toxin)? Definitely. The spores survive direct heating/boiling, very low pH environments, and desiccation. For instance, botulism from canned foods can occur from eating the food (and toxin) directly - but you're supposed to throw it out if it look suspicious because even if you cook it and inactivate the toxin, the spores are still present after cooking. The spores can find anaerobic environments inside the body and germinate, then produce toxin afterwards.


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