I agree about not feeding it, if you have any ? about it at all. But telling you to just "throw out" a ton of hay is ridiculous. Call your supplier, tell them you have concerns and see if they will buy it back or at least make good on it. I am picky about my hay and when mine got wet a time or two it was grass hay, so I was not concerned. I am allergic to hay and really allergic to mold and mildew, I sniffed mine first, did not have a reaction and it really smelled like damp hay to me (which I describe as musty) so I chose to feed it. If I had started sneezing, or having an asthma attack after sniffing it, I would have called my supplier and even though it was my fault it got wet from rain, I guarantee he would have made it right for me.. A good supplier will take care of their customers, especially someone who buys that much at one time.
All replies that say it is best to not feed it are completely correct.
That said, however, you asked a specific question, is a little bit okay? The answer is always qualified. But, yes, horses can eat some moldy hay without harm.
What causes the harm is a combination of several things, not all of which relate directly to the hay. Horses have a very sensitive gut; however, it is not typically the gut that is at risk. It is the lungs. Someone answered that moldy hay causes respiratory problems, and they are right. It is the inhalation of the mold spores that causes problems in the lungs. The symptom you will see is a hoarse coughing or wheezing.
But that's only part of the story. Horses that are kept in stalls and barns are at the greatest risk, while those that are free pasturing are at the lowest risk. The reason is that the stalled horses are kept in conditions where there is constant barrage of dust, and they never get the chance to clear their lungs. The mold spores can be the card that tipped the stack. But horses that are free pastured can go to a big round bale, eat some hay that has some mold in it, then get away from it and clear their lungs. We have had horses that inhaled enough mold to get the cough, but within a few hours or a day or two, they cleared right up.
So, while I would make every attempt to locate the worst part and extract and discard it, you can, in a critical need situation, go ahead and let the horse eat some of the affected hay, especially if they are kept out doors.
Typically "black spots" to me would mean badly deteriorated, rotted spots, which were caused by excessive contact with water to the point that the grass literally rotted. This is beyond mold, and should never be fed. However, if a horse encounters it, they will generally drop it from their mouths, and it doesn't pose much a risk to either gut or lungs. But, that kind of bad hay is usually easier to locate and discard than the more insidious internal mold, which is harder to see, has tiny white specks instead of black spots, looks like dust when you open the bale and the pores get blown about, and smells musty. That kind is harder to get all cleared out of a bale, and is the type that causes the lungs more problems.
From the pics it does not look that bad to me. I got some earlier this year from my supplier, it was sunbleached from last years cutting. My horses did not care one bit, they ate every last scrap of it. If it is a bit moldy, it is likely from not being stored properly from the field. Alfalfa should be stored, cut side down.
Your hay was not properly cured before baled. Could have had a light rain, heavy dew, or just simply baled too soon. Making horse quality hay takes knowledge, timing, and a lot of prayers to the man above to hold off the rain.
I don't know, from what I'm seeing, it looks OK actually...
Camera focus and color corruption could be masking something though.
Is there any dust if you were to take a flake and pull it apart vigorously?
Do you have any horsey friends that could come and take a look and give their thoughts on it? That would probably be your best way of figuring this out.
Yup, it's definitely not going to win prizes at the county fair (got damp, or just sat too long in one place, before baling)... but I am not seeing anything (from the pics -- remember, this is different from being there and seeing/sniffing it in person!) that would make me not want to feed it to the horses.
If you're talking about the little indistinct darker areas on the leaves, it does not look like mold to me from those pics.
I agree with whoever said to take your "worst" parts, and some average parts, to a really good local horse person and see what they think.
I did come into white powder stuff in this hay and the no one got that part. All in all not much wasted and everyone is doing great except they are not happy we are out of alfalfa at the moment. Any I gave to my horse, I made sure to shake it all out first but she mostly has been getting grass hay this whole time.