The first thing to go wrong was her right side, I ran my finger down her spine on that side to check for soreness and she scrunched up her muscles, hollowing her back. I stopped riding for two days hoping to go get her stuff and not aggravate the soreness. Four days ago her left side went stiff and ouchy as well. She's laid-back and doesn't go much faster than a walk and the infrequent sprint in pasture, so I lunged her once and rode her on a loose rein and did more bending and lateral work to try stretching her muscles. She had a swollen, hard left foreleg cannon bone area that day that didn't seem to bother her. She gets scabby lumps from fly bites so I figured the flies had irritated her leg. She was also taking shorter strides with her left hind, not surprisingly.
Yesterday she walked up totally lame in the left hind, the swelling gone in her foreleg. She limped, nodded, and kept her heel off the ground with her toe pointed, if she had to walk she would take very short steps with the leg while her other hind reached farther directly in front of it. I let her have pasture again, and in the evening saw that she was worse than when I left the gate open in the morning, so I kept her in her stall for the night. Today I came out and her left fore is swelling again, but her left hind looks better. I lunged her for a minute w/t to check; she's perfectly willing to move and stretch to the ground on her own time like usual, took short steps in the left hind for the first strides but after trotting four laps didn't have any noticeable fault, and then tracked up at walk with a short step once or twice. However, when I stop her she keeps her left hind farther underneath her instead of keeping it where it should be for a square halt, and then bends her leg to keep her heel off the ground. When asked for a side pass to the right she grunts and limps, really not wanting to put her left hind hoof flat on the ground for longer than a second.
Oddly she wants to pick up her right lead more than the left for canter. I saw her canter homeward yesterday and it looked like hell; real short and choppy. When she urinates her forelegs shake. No change in behavior, no heat in any part but the heel of her left hind. She lets me pick it up but leans on me.
So... Does this sound like only arthritis and plain asymmetrical muscle problems? Or something else? She wasn't lame before I put her on the MSM and other things, just stiff. I wonder if she could have strained something trying to show off to the new mares nearby. We've had rain, cold, and swarms of insects lately.