Sorry, but I don't completely agree with your Vet. I don't think it's hereditary as such - but I had a pony with COPD for many years - and it was common in his family line. Don't know if it was passed on by the female or male side of the family, so can't help there, but there certainly seemed to be a predisposition in his bloodline.
I think it would depend on the severity, and what the job of the offspring would be. I’m sure I’ve read there’s a genetic element even if it’s not guaranteed.
Severe COPD, and wanting a sports horse/competitive offspring would be an absolute no. But a mild, easily manageable case and aiming for a happy hacker or low level horse, I would consider it if the mare was otherwise a very good choice to breed from.
My gelding had it last year and (touch wood) it hasn’t appeared again. Some of the other horses in the field also had an increased respiratory rate, but he seemed to be especially sensitive to whatever it was in the air. A vet suggested it was possible he had strangles as a youngster (Irish bred) and it weakened his airway’s defence system. He’s a gelding, and a crock in other ways, so multiple other issues stopping him breeding... but if a nice mare had his level of asthma, and it didn’t reoccur, I’d be happy to breed from them.
