I've always had mares and never had and issue with colic and the estrus cycle.....until we breed my daughters mare and got a filly......in the February of her 2nd or 3rd year she started picking at her food, it lasted about a week and one night near the end she started having a hissy fit, bucking and carrying on in her stall....this mare is a bit of a princess and this was her expressing that she was in pain.......we walked her and gave her banamine per vet instructions.....she was fine 24 hours later......fast forward to the next February.....same thing only no hissy fit and no banamine required......the next February same thing but not quite as bad as the last year......fast forward to this February.......and we had no signs of colic at all........we concluded that it was her first cycle that causes all the discomfort and now that she is 8 she has out grown it.
I wonder since your mare is older if she now has some sort of cyst on her ovaries that might be causing her pain during her first cycle.?
The follow-up vet appointment was today. She agreed that hormones are the problem. One of the first things she said was that my mare is a good candidate for spaying; she said there's an excellent reproductive vet at WI Equine Clinic that does it intravaginally, which has a reduced risk of complications and faster recovery time for the mare. She will be sedated and given a local, then stand in stocks for the surgery.
We discussed hormone therapy. The vet said we can try progesterone injections but she needs to stay on them given the severity of her colics. We covered a lot at today's appointment....oh yeah, and the vet said it's very possible the ovarian pain is giving my mare ulcers or "just about there", and since I have the probiotics covered, she gave me a tub of equine antacid (SmartGut) to start her on immediately. I am to keep hand-walking her when I don't ride...and also hay changes are to be done very gradually. The vet will email me later and be in touch regarding the hormone therapy/spay (I asked for a quote).