[Katherine Fraser]

Chilly is a 3yo Border Collie spayed bitch.

She becomes stiff esp. hindquarters when exercising, esp when excited. It used to happen only when very hyped, eg throwing a ball or training agility. She would become hyperthermic(T42) and ataxic.

In the past year she has become much worse as she now becomes stiff-legged after normal exercise, without becoming hyperthermic. A year ago she would run 10km+ with me with no problems. Now she can only manage about 6km before becoming stiff-legged and wobbly.

The stiffness doesn't seem to worry her when she's not hyperthermic as she jumps well and runs around quite happily. However I do think her condition is heat-related, as she is much worse in summer. Also the condition does not appear at all if she can jump into water while exercising.

I have x-rayed her hips,spine and neck. All normal. I have done post-exercise blood tests for electrolytes, and muscle enzymes. Also bile acids, all normal.

She has had 3 episodes while training agility at our club, where she was stiff-legged, struggled to jump, and seemed to "switch off", and wandered off the course, and seemed vague and unresponsive to my voice.

In every other respect she is a lively, healthy, happy dog.

Any ideas?