Do you mow the pastures? Tall, older growth is not attractive to horses because it is tougher than new growth. 3 acres is a sizable field for 2 horses, you may not see where they are grazing because it is so spread out. Mowing regularly helps keep new (preferred) growth all at a similar height. Regular is when grass gets about 8 inches high, mowed to 5 inches so roots are not getting sunburned, leaf loss is not a shock to the plant, and dirt is protected from heavy rain. Regular is not timed by days, just grass height.
Did you do a soil test? You need to fertilize by what the grass needs, not using generic fertilizer mixes sold at the store.
Wondering if your horses are older? Many get quite lazy, don’t want to walk out to graze. They will stay up close to eat the hay.
You did not specify your Midwest location, but I quit mowing pastures around Labor Day, so grass can get some length before it normally gets really cold here in Michigan. This year is plain ODD, from spring to now! Dry or wet at funny times of the season. No sun, cold that is not “normal timing”. Grass has still done quite well here, still growing productively until 2 weeks ago. We started putting out some hay then, but it is not much because they are not cleaning it up. Hay at night in stalls is cleaned up. Still not a great amount yet.
I would greatly reduce hay fed outside, see if they will turn to grazing. Horses are unlikely to “starve” themselves when grass is available to them. Have you walked the field, to see grazing areas or lush growth spots, see the types of plants in them? I see the variety of growth when i mow or walk checkling fences. Some places growth is too short to graze, jus has green color. My husband thinks our pastures NOW should keep the horses fed! No, it just LOOKS green, not much height except in the potty areas. They need some hay, not a lot, but some.
A soil test should help you with minerals needed to grow good grass. You want to avoid Urea in your fertilizer, it can cause lameness, especially when heavily applied. Check Urea Poisoning on Google. I use Ammonium Sulphate instead as my Nitrogen source, because it has no such side effects. Price runs about the same.
You want to check any Clover you seed. Red and white flower Clovers can cause horse problems, especially in warmed climates. All turn up in common “pasture mixes” because cattle, sheep, have no issues with them. I have turned into a “very picky person” about reading seed labels. Amazing how often there is seed you don’t want in a bag! We have volunteer Clover that just appears in the pastures, and I am seriously trying to kill it in the hayfield… Not always sure of the kind because pasture mowing helps prevent the slobbers and we have very little white on our horses to get the photo sensitivity problem. That is a very time consuming issue to deal with!
