Yes, the heat sterility is definitely a thing. Once you get five days in a row over 85 degrees F, or three in a row over 90, the bucks are often sterile for the next 6-8 weeks. Once the season progresses towards winter, many rabbits choose not to breed, nature's way of avoiding cold winter babies. And some bucks are just so laid back, they just don't care. I loved the gentle Champagne d' Argent rabbits, but the bucks just had no interest in breeding, so frustrating.
A few things I tried to help the situation: 1) After an attempted breeding, leave the buck in the doe's pen, and take the doe to the buck pen. It gives them a chance to smell the other animal's scent overnight and hopefully get in the mood. Then, take the doe to the buck (who is in her original cage), and try again. Whether it works or not, I return the buck to his original cage.
2) Try for at least 14 hours of broad-spectrum lighting, to simulate the arrival of spring.
3) Did the rabbits gain weight over the non-breeding summer? If so, additional exercise may help the issue.
4) Check the doe's vulva. While rabbits are induced ovulators, they release eggs as a result of breeding, instead of having heat cycles like most pets, farm animals (and people); there is also a mini receptiveness cycle, about three days or so. When the vulva (the 'slit' beneath the anus when you flip the doe over) is pale and thin, she's really not in the mood. If it is very dark purplish red, she's probably just past 'the mood'. But if it is gently pink/purplish, a bit swollen, and moist, she's more likely to be receptive. Bucks are often not interested in non-receptive does.
5) Bucks can be easily discouraged by aggressive does. If you have a timid buck and an aggressive doe, you may need to wait until her cycle shows a moist somewhat purplish pink vulva, so it is more likely she is indeed receptive and not just domineering or grumpy, and then hold her for breeding so she doesn't attack the buck right away. Some bucks prefer the aggressive does, and get excited by the challenge and chase; but others are totally cowed by the experience and refuse to even try to breed.
I like Rosey1's suggestion to try switching buck houses, and see if the smell of the competition would put them more into the mood. I may try that. Sometimes it just takes time for the buck to get back in the 'mood'. I also like RabbitsoftheCreek's suggestion to let them run around together in a safe location for a period of time. I've never tried Ladysown method of separation for two to four weeks, very interesting. It's good to have a variety of tricks in your arsenal when dealing with recalcitrant breeders.
