The vet came out this morning to do x-rays on Dawn's front feet and lower legs to see if we could determine what was causing her lameness, or to rule certain things out. Dawn patiently stood for the full series of x-rays, including having to stand on the little wooden blocks for the shots from the sides and back, and standing with one foot at a time on the flat x-ray holder for the navicular shots. She was a trooper, standing like a rock despite the other mares still being out in the pasture.
The good news is that nothing of concern showed up on any of the x-rays. She's got the slightest bit of remodeling at the lateral edge of the pastern joints, but that's not unexpected in a horse of her age and conformation - her front legs aren't perfectly straight from the knee through the pastern and foot - there's a little bit of a twist in there that puts some lateral pressure on her joints and feet. This structure is why she has a bit of a paddle in her trot. The minor changes shouldn't be enough to cause her trouble, although they may worsen a bit with age. Her tendency to really slap her feet down also puts extra wear on her joints. Other than that minor flaw, all the x-rays looked really good - she's got good clean joint spaces throughout her feet and lower legs, and the navicular bones were smooth and just fine - no roughness that could cause soft tissue problems.
The vet will be sending me the x-rays on disc so I can keep them for reference, and will also send me her list of things to screen for in a drug test on a pre-purchase where I'm concerned drugs might be an issue. I'll probably have all horses tested for Ace, Banamine and Bute, but will do a more rigorous drug screen if I've got any doubts about the seller.
The vet also repeated the trot-out followed by flexion of the lower right leg joints. Before flexion, there was only a whisper of unsoundness ever 3 or 4 steps at the trot, and even after flexion the unsoundness was pretty minor. This is all really good news, and probably means that she just pulled or tweaked a soft tissue structure inside her foot - a tendon or ligament. Those soft tissues of course don't show up on x-rays, although they do on an MRI, but there's no need for that since she seems to be be recovering well. The vet said I could ease her back into work. I'll keep walking her through Saturday, and then she'll get a few days off if I make my horse search trip to Minneapolis. If she's doing well when I get back, we can try a bit of trot work and see how she does.
Considering that the report from this morning's turnout - the mares went into a new pasture, and there was a large coyote to herd, and there was much galloping, bucking and general cavorting on Dawn's part, none of which made her worse - I'm pretty encouraged!