You will get umpteen replies to this question ! I have always done my girls after the first season, as my vet recommended. All 3 have been fine afterwards.
You're right EDP, there are widely differing opinions. I've been told to leave it until around age 2 when the girls are mature and have more or less finished growing. That makes sense to me, but I think as long as the girls have at least one season it's all good. Since I'm breeding my girl, the situation hasn't really arisen and I'm absolutely no expert on the subject of spaying.
I have heard that experienced breeders can actually tell the difference by looking between a lab spayed early and one spayed after growth is finished at two years. And some say that particular kinds of injuries happen more with early spays. I am no expert but I have my pups best interests in mind which is why I asked.
It is a minefield of options and advice, but I think everyone has their pups best interests at heart with their decision making.
I made the mistake of getting my lab spayed before her first season on the advice of the vet at that time. She had cruciate ligament disease and various other issues shortly after - I know it may not be down to that but I did some reading way back and it suggested it may well have been linked. I’m going to let my new pup have at least one or two seasons ( the breeder has advised 2).