I'm sorry if this is in slightly pigeon English; I usually talk horses in French!
We have an 8-year-old Spanish/Arab mare who we would like to breed. In April 2009, we took her to be mounted by a Lusitano stallion three times while she was on heat (obviously). We were pretty sure she was pregnant - she gained weight, her behaviour mellowed a little bit and she no longer came on heat. However, in the middle of December she started to 'flirt' with the geldings and just to be sure, we did an ultrasound which showed that she was not pregnant.
The following year (April 2010) we borrowed the same stallion for a period of six weeks and left them together (alone) all the time. She was on heat for about 12 hours during which time he mounted her countless times. Still not pregnant.
The vet can't see anything obviously physically wrong with her, other perhaps than being a tiny bit fat.
Has anyone else had the same kind of experience? Is it worth our while trying again this Spring? Any advice or suggestions gratefully received!