Don't know if it's been identified in cockers or not, but what you're describing doesn't sound like it. The hind end collapses while they're still trying to run in front. Here's video showing the characteristic progress of an episode -- it's very disturbing at first glance, but then you see that the pup keeps on wagging, fetching, and looking perfectly happy even while she's dragging her hind legs. It doesn't seem to bother THEM - just their owners!
Exercise Induced Collapse
The University of Minnesota Vet School is the outfit that isolated the gene and developed the blood test.
I could only watch a couple of seconds of that video.
You are right. That ain’t my little boy. He’s just lazy. I don’t care.
I love him and sometimes they what they is.
thanks for the video, erh, sort of.
Thank you.