I suspect that what people call "canary grass" might differ...my hay supplier replaces bales that accidentally have "canary grass" in it. But I did see hay on craigslist recently that was a mix of grasses including canary grass, and written in such a way that it was a good thing.
Curious what the hay experts will say. My horses don't really eat the "canary grass" that comes in our hay sometimes....so I'm not sure what it really is.
ETA: sorry, I realize my response is useless. But hoping someone else will chime in to help.
As a personal anecdote...I have some wild Reed Canary Grass in my fields, and the horses love to nosh on it when it's young...once it gets older/taller/rougher, they don't like it as much. I do have my field with Reed Canary Grass baled because when it's older, it's quite low in sugars, and I'm able to feed that particular batch of hay to my IR/Cushings mare, without any soaking necessary.
Interesting, I wonder if the cutting # matters? I generally buy a 1st cutting timothy from my hay guy, but getting the first cutting in can be tricky if it's been a wet spring...sometimes it can be cut on the late side. Maybe that is when canary grass is not very palatable - if it's tall and mature? But if the same field was baled as a 2nd cutting, I suspect it could be very different.
Reed's Canary Grass is a type of orchard grass according to my main hay guy. It needs wet ground to grow. It's not a very common hay here in the Mid-Atlantic because of the specific growing conditions needed. Once it's cut, it needs to be baled within 3 days (according to him) or it's reduced to the palatability of straw and is then really only aggreeable to cattle. All of my horses eat it very well, but I have one mare that LOVES it. Whenever I come across some, I buy enough at least for her. Nutritionally, I was told it's about equal to regular orchard grass.
I asked about Canary Grass Hay a few years ago, on another forum and got a couple replies from people who had used it. I knew these two personally, so their remarks stuck in my head.
One said her animals wasted most of the hay, didn't like it, only ate it because nothing else was presented. She had to up the grain, because they were not getting enough ingested to keep the weight up. She didn't have anything else, not enough budget to go get other hay. She strongly recommended against it unless I had SUPER EASY KEEPERS, who could manage on less hay, while wasting the rest.
The other managed a Fjord farm in the Midwest. They produced an excellent line of Fjords, well trained and usable. She said one year they had a bad drought, with very little hay produced on the farm. They had Canary Grass growing well in the usually wet areas, so they decided to cut and bale it for hay. They cut before it was fully mature, and fed the Fjords the Canary Grass hay over the winter. She also said there was a fair amount of wasted hay, but the ponies ate it and came into spring in good shape, though no fat ones. Foals were in excellent shape when they arrived and no equines went hungry with the Canary Grass hay in front of them. Importing hay was out of the price range they had in the budget for the animals. So they had to make do with what they had, which was the Canary Grass in the fields to bale.
I passed on buying the local Canary Grass hay though, after these reports. I don't buy hay that the horses will waste, if I can avoid it. This seller wanted the same price for a bale as the better grass mixes available to me. No bargin there.