As suggested in an answer on [Gardening](http://gardening.stackexchange.com/questions/11007/what-plants-or-gardening-additives-might-cause-the-specific-neurotoxin-symptom/11027#11027) damp hay can grow molds, some of which can be toxic to animals and humans. 

[trichothecene mycotoxin](https://en.wikipedia.org/wiki/Trichothecene) can have descending paralysis as a symptom, but it looks like it also includes digestive track hemorrhages, which was not evident in any of the 3 individuals described in this event. While probably not the solution to this issue it may be involved in similar events.