What is good hay?

Good hay is when I can look at my mow and breathe a sigh of relief. I know what we grow so I know its composition, but getting it in well is a crapshoot. It's haying time once again. It's a nerve wracking adventure that is at the mercy of the weather, just like any farming.
But when it is the largest component of our horses' diets it is well worth learning as much as you can about it.
As a horse owner, what do I need to know about hay?
If I was boarding my horse, I'd want to know about price. My board this year is likely to go up because hay is in short supply and the price will reflect this. Hay acreage is down as many farmers turn to corn this year, and the hay export market has developed quite well and offers us competition for our excellent Ontario hay. Good for farmers, not so good for us. There's also been a drought through the spring, making yields go way down in many fields. We pulled in 90% yield compared to last year but I have heard reports of as little as 1/3 yield compared to last year.
Hay will be more expensive this year, but beware though of buying based on price. There are many who will take advantage of the higher price and try to sell you baled weeds.
Question to ask your hay dealer: What is the composition of the hay? If the answer is "I don't know," keep looking. (Yes, that was the answer I got from one guy last year who was charging $4.50 a bale - it had pieces of wood in it and it looked like he'd baled his barnyard!) Watch for weeds - not only do you not want your horse eating unknowns, but you don't want those weed seeds infesting your pasture when they come out the other end.
What size is the bale? A forty pounder is easy to handle but the size be should reflected the price too. Also ask about fertilizing. Does the field get regular fertilizing or is the nutritional value getting depleted by continuous harvest? If you get a strange stare, you know the answer.
For hay quality I'm looking for green and clean. Green means it most likely didn't get rained on, which interrupts the curing process in the field and you end up with bleached hay when it has to start curing all over again. Clean means it doesn't have mold growth, which means it was put up at a good moisture level (14.5% is the charmed figure). Cattle farmers have a hard time understanding horse people, since their priorities revolve around alfalfa leaves: They're focussed on the nutritional value where I'd rather have the hay a little drier, lose a bit of leaf and supplement nutritionally than have a bit of mold. It's all a trade-off. Talk to your farmer. 
There will likely be a lot of dust in our hay this year as our grasses headed out early and the seeds will be dusty.
Is a hay analysis available? It only costs around $50 or so to analyze the hay and it's easy to do, and it is a valuable tool, not only to the farmer who can detect deficiencies, but to you when you can take that analysis to your feed dealer and have them make recommendations. Many people are overfeeding, trying to compensate for unknowns, but it can save a lot of money to target your nutritional requirements to feed more accurately to your needs. My horses survive on nothing else but a ration balancer and a few extra calories for the nursing mare, although we do have easy keep Paints. For us, we harvest about 16 acres so the cost is about 3 to 5 cents a bale. Not a lot in the larger scheme of things.
A hay moisture meter has helped us to make decisions when haying, keeping any suspicious bales near the door or outside where we can deal with them easily if they overheat. They're around $180 at TSC, an investment that might be helpful if you're taking hay straight off the field.
This year we've gone to round bales and although we haven't figured out a system to feed them yet I do have a few observations so far. Myth: round bale hay quality is poorer than small squares. Not necessarily. If the hay is managed the same it doesn't matter what format it's stored in. Keep it covered or inside, bale in the good timing window, and monitor the quality as you go, which is something that is admittedly easier to do when you're handling small squares. I like the labour savings, and while it doesn't make the best use of our storage facility we can stuff enough in there to do us for now. One observation we made was that there was no chaff on the wagon, which means that good stuff is better held in the bale in rounds than small squares.
Get your hay now if you can. It is going to be in short supply this year.