I am hearing a lot about impactions this time of year and had trouble myself. My vet said the hay type did not matter but are there other opinions on this. I was told to feed a little, but not too much, alfafa.
Typically, post surgery you will see the hospital bungie flakes of hay on the OUTSIDE of the stall bars so the horse can get little bits...and most often I've seen either timothy or afalfa/combo.
Many years ago, the Va. Tech Veterinary School (EMC at Morvern Park in Leesburg, VA) did a pretty exensive study on the incidences of colic at a myriad of farms of varying mangement -- including hay types they fed.
They found a higher incidence of colic with Orchardgrass -- but clearly the major factor was management (that is limited turnout, lack of fresh clean unfrozen water 24/7 -- that oten occurs in the winter/cold months.).
I don't think it is the choice of hay that is a problem, but the way that you manage feeding can be. One example being; when you get a new load of hay do not just feed the new hay without mixing it with the old for about a week, to make the change gradually. Horses can colic when given the same type of hay, that has been cut from a different field
My vet always recommends a little leafy alfalfa post colic, also she recommends lite hand grazing. Doing this has always worked well for me for a few days (if a true impaction. not gas) gradually working them back to their regular hay
I'd follow your vet's advice but it would help to monitor your horse's water intake and offer him some warm mash in the winter. If the water is typically cold, your horse/s may not be drinking as much so it may have more to do with less water intake than variety of hay.
Having been through two colics (one requiring surgery, the other a week in the clinic) - this is what I've found.
Soak all feed. Gets additional water into the horses. To give you an idea, my horse eats 1 quart TC Senior and I soak it with 1.5 quarts of warm water (I use old Gatorade bottles; they're tough plastic & I can fill them up and take them to the barn easily). It's like soup at first, gets to a wet oatmeal consistency in a few minutes.
Hay: Nibble Net. Best invention ever. Doesn't allow the horse to eat huge mouthfuls of hay - huge mouthfuls that might get stuck! Before the Nibble Net, my guy would finish 3 flakes of hay in about 2 hours. Now it takes him about 5-6 hours. I use the NN with 1.5" holes.
I especially like the Nibble Net when my guy has to be stalled (weather, etc) as it allows him to "graze" just about all night like he normally does (he generally lives out 24/7).
ETA: I have not found the type of hay matters as much as the texture. Stiff, stemmy flakes tend to be harder to chew, can cause sores in the mouth that can lead to less chewing... you get the idea. I have always fed a timothy mix or a grass mix - as soft as I can find. Usually pay more/bale, but it's better than a clinic bill!
I second tarynls - wet feed and controlled hay. Electrolytes wouldn't hurt either.
The first year I had my pony, she colicked and needed surgery. The new barn we moved her to post-surgery was kind of afraid to feed her though and she ended up getting thin - we moved again and she was much better since she came up to college with me where I could keep an eye on her.
She was also on 24oz beet pulp & 24oz regular grain - the beet pulp made her grain nice and soft.
Now, my pony gets her food wet down (hf of senior) at each meal and gets an electrolyte supplement in the mornings to encourage her to drink more. For about $0.27 a day for her electrolyte, I'd rather be safe than sorry.
Well stay away from bermuda hays. I've never heard of colic problems with orchard though. I feed that now but am going back to timothy.
I recently spoke to 2 different vets, one from the Univ. of FL. & one from Palm Beach Equine. Both said to try to stay away from bermuda hays due to the impaction problems.
I had a vet at a clinic (we had brought friend's horse in because of a bad colic) tell me that feeding coastal hay increases the chances of impaction, especially the round bales. Down here, our coastal is basically devoid of nutrition; the only person I know who fed it used it as a filler/something to nibble on in between her horses' "real" hay.