We have fed off round bales for years (taking sections and feeding them out). If its a little musty looking its okay as others have said they will eat around it. If its black don't feed it toss it. I knew someone who let their horse eat funky black hay and the horse coliced and then went septic. The horses body swelled up and the horse ended up being euthanized. So, don't feed black hay.
Botulism is caused by a toxin that is closely related to same bacteria that causes tetanus. I think it may even show signs that are similar to the tetanus infection but it is much more lethal. It is one of the most potent toxins known, and small amounts can be deadly to animals and humans. Horses are particularly susceptible.
They can get it from a few different ways I think but the concern is from eating the rodents or small animal carcuses that can sometimes end up in a bale of hay. I think they can also pick it up from eating the hay that's been trampled and peed on....
I have been feeding round bales for years for about 4 years we bought rounds that had been sored outside. We just put them in the feeder and horses picked through the yucky stuff. Quit buying stored outside hay was way to much waste will only buy rounds that are store inside. The last year we bought stored outside hay my mare with heaves had a real bad heave attack from it. Had a barn full of rounds we couldnt feed so never again will I get stored outside hay not worth it.
There is a part that is black on the round bale that is where it was layed on the ground I believe. Horses didnt touch it though. They ate right through the middle to the good stuff Posted via Mobile Device
Or you can be like me, I will not buy round bales unless they are stored under cover and on pallets. Most hay growers here market to horse owners and do store all their hay that way. Posted via Mobile Device
I buy round bales that have been stored in a shed and are considered horse quality, which means they weren't left out in the weather.
I don't free feed though because if I did that, the bales would only last about 10 days. If I keep the hay in my barn and peel the hay for morning and night feedings then I can get away with feeding one round bale for almost a month. At fifty bucks, that's a huge cost savings for me....
Like others have said, if you give them the choice they will pick around the bad parts. They always want to eat the goodies first. Like when I feed Alfalfa they toss the stems out of the feeder to shake the leaves off and eat those first then clean up the stems.
None of the round bales I have fed have been stored inside. They usually just have a bad spot where they have been sitting on the ground in the stack yard. If you are that worried about it, you can pull that part off.
We never feed any hay that has mouldy or rotten sections in the bale. Your horses may pick around the bad hay, but don't forget that their heads are buried in those bales, and they are ingesting/breathing the mold spores. While it's true that mould is everywhere, and is somewhat unavoidable in smaller amounts, by feeding round bales that have visibly mouldy spots, you are asking for trouble.
We put up our own rounds and squares, always stored on pallets, always under cover right away. I will not take a chance with their health like that.