You commented once that somewhat moldly hay would most likely not cause colic or digestive problems with horses but the dust was the issue. It might affect the respiratory system instead. Did I understand that correctly?
I have a little mold in some 3ft by 3 ft by 8 ft orchard grass and timothy hay. It was put up dry I thought when we baled it. This is a surprise to me.
Horses eat it fine but wanted your opinion.

thanks,

Jim,

This is a response that Dr. Valentine gave me when I asked the same question. Hope it helps.


I posed the question of whether moldy hay really caused colic to my equine practitioner colleagues, and got a lot of interesting answers. Apparently there is one study from long ago that linked moldy hay to increased risk of colic, but some questioned whether this link was really justified. No one knows of any mycotoxin (toxins made by molds) in hay that would directly cause colic. The potential for a sudden change to moldy feed to cause colic by being a different feed is there, as is the potential for a horse not eating enough of the moldy hay to keep digestive function working properly, leading to colic. I think the major risk of moldy hay is to a horse's respiratory system. A horse with respiratory allergens could react badly to mold dust in hay, and could cause allergies in some horses. Shaking it out will help, and definitely discard the worst flakes. The risks there, but these measures should minimize them. Keep close eye on how much your horses are eating and also for coughing or other signs of allergic reactions.

The question of whether moldy hay could cause colic proved to be an interesting one when I posed it to lists of equine veterinarians and veterinary laboratory diagnosticians. Some felt that this was true, but it seems that only 1 scientific study made this connection and it was not the most solid of studies. I suspect that the big issue for colic may be a change in eating pattern if the horses do not eat the moldy hay as well. If you feed this I would suggest soaking in water first, and discarding the very worst affected hay. This is what I have done with my hay for some years now.

Thank you for the responses Lori and Dr Beth. This confirms my own thoughts.
JIM