You will get many varied responses to this question.  I am 200% against alfalfa unless it's being fed to a hardworking performance horse; i.e. cutting, reining, hunter/jumper, etc.

Alfalfa is a very rich hay and not something I have ever fed.  Whatever part of the U.S. I have lived in, my vets have all told me that I can't use my trail horses hard enough to burn up all that energy.

It sounds as if your horses are fairly easy to keep in shape, so the less they get in terms of excess protein, carbs, and starches and even fat, the better off they are.

IMHO, that means no alfalfa and  a small amount of dry grain to add their supplements to.

I have four horses.  Two are downright fat, the other two only slightly raise my vet's "fat" eyebrow.  Two get 12 ounces of dry grain 2X/day; the 16H horse gets 14 ounces of dry grain 2X/day; the rescued Arab gets 12 ounces of Purina Senior 2X/day.

They all get some type of supplement added and I don't over do that either.  I give each one what they need for the moment ---- which could change by Fall because two horses are 21

What makes up hay varies depending on the part of the country you live in.  Here in the west. Alfalfa is the prevelant forage crop that is put up as hay. It's fairly drought tolerant, having deep tap roots. It produces 3-4 cuttings a year in my area a stand of alfalfa will last 10-12 years with out having to be replanted. The long dry summers here with little humidity allow it to cure well in the cut fields. There are a lot of horses around here that get noting but alfalfa and do just fine. And I can point you to several local vets that say it's just fine as a forage for horses.

Alfalfa is much higher in protien than horses need. Good dairy quality alfalfa is 19-22% protien. A horse can do very well on a 7-10% protien grass hay. The excess protien is converted to amonia and pee'd off in the horses urine. Which requires the horse to drink more water to stay hydrated.  Also horses on a high alfalfa diet seem to produce a heavier lather for sweat. This is less efficient than the more watery sweat by horse not eating alfalfa. Alfalfa is also typically higher in Calcium. This some times upsets the Calcium/Phosphorus ratio. There are many suppliments that can be feed along with alfalfa to correct this ratio.

Alfalfa is paletable, highly digestable, usually contains more cell solubles, less cellulose, higher protien and lower fiber than grass hays. A horse that picks at his feed to consume 20lbs of grass in a day may readily consume 30 lb of alfalfa if given free choice. If you don't offer free choice feed, the horse may consume his daily ration faster and have more idle time. And my horses seem to get in more trouble when they have idle time.

Do a search on the internet for Alfalfa,

http://www.shady-acres.com/susan/alfalfa.shtml

http://www.alfalfa.org/pdf/Alfalfa%20for%20Horses%20Revised.pdf

If your pastures are in good shape, you probably don't to feed any additonal hay. Save it for later when you might need it, say if it gets dry and the pastures are gone. I can't see a bit of grain will make them hot but additon of some oil will help keep the coat shiny.

As for alflafa, thats all I feed. It doesn't cause them harm, hottness,excessive urination or sweating. My horses are arabians, I show them and they are very reasonable, even temptered horses. Alfalfa seems to get a bad rap especially from those who have never fed it.

Yeah, you're gonna get alot of different answers, but here's my question, why are you feeding extra hay if you have good pasture hay?

We have awesome pasture, we irrigate 100 acres by hand for 6 months or a little more out of the year, and we only feed oat when pasture is done for those few months and a small flake of alfalfa when we have "really" and I mean it;'s gotta be really cold days to give them a flake of that. The supplements they get is a handful of all-in-one and mix in a multi-vitamin, and msm to the ones that need it and that's it. Rountine worming every 8 weeks, WNV 2x a year, and 6 way once a year, oh, and their once a year float.

If need be let them graze on the pasture if it's a good pasutre and bring them in at night if you need to. Ours are on it all day, but they are working ranch horses, so it's worked off really quick and they are in the mountains alot also.

Hope some info helps, gather some from everyone and maybe watch your critters and see what will work for yas!

I used pelleted alfalfa when living on the circuit shows during summer.  I fed grass hay but kicked it up a notch with alfalfa pellets for the shiny coat and trim underlines.  I also showed working horses driving, jumping, etc.  No horse in my barn did less than 4 events, some close to 12...they earned their oats.

If you like how they (yours) look and act then don't mess with alfalfa.  They (yours) are already on grass so just add grass hay at shows to keep their tummies full.  I don't mess with what works...I'm like Dr. Phil.