A question was asked about how late to breed outdoor rabbits with the heat of the Summer coming. The answer depends on a few things.
First of all, heat doesn't have to affect late Spring (here in the northern hemisphere) breedings as long as the management of the doe is good and the weather is not brutal. Since we can't predict the weather, we have to assume it will be brutal. In that case, you need to have an alternate cool place for the doe to kindle and spend the first week or so with her kits. That's the easiest way to answer the question.
So, what does heat do that is so bad?
First of all, it put a tremendous strain on the doe. Dealing with the heat AND growing pre-born kits will make her cranky and she may go off feed. Pregnant rabbits that do not eat and drink well can develop toxic symptoms within a day or two and die. The last week of pregnancy is a poor time for things to get bad. You will want all conditions benevolent during those 7 days. I have lost 2 does that stopped eating during pregnancy and it was hot. Does that slow down on food intake need to be fed carefully and with apetizing fresh foods to keep them from developing toxemia. Once the kits are born, does get naturally hungry in order to produce milk, then things return to normal, but in the interim each day is a challenge.
Heat increases the incidence of flies and bacteria. Back in the 90's, I lost 3 newly born litters during the heat due to bacterial invasion. And it happens very quickly and to large litters. I remember one litter of 13 French babies. ALL were fawn or creme (they were beautiful!). The temp hit 92* (and stayed there) when they were 6 days old. They developed diarrhea and started dying in 24 hours. Over the next week all but 2 from that litter were gone.
Heat causes a temporary sterility in older bucks for several weeks after the heat spell. I plan to have all my breedings done by June 1, for that is when the heat CAN start up here. We usually don't see weeks of 90* until July, but a few serious days of 90* can theoretically disrupt your breeding plans. So, keep the breeding bucks cool as long as you can while you work into the late Spring.
That said, I have two final early Summer litters I am waiting on. The first is Liebchen, who is pictured above. She is due on July 2, but last time went 5 days past her date, so we'll see. She has had two false pregnancies this spring, so she may not have taken. Next year, at age 5, I will be sorry to retire her. When she was 6 months old, she stripped every shred of fur off her body to make a nest after the rabbit in the NEXT cage was bred. This doe loves being a mother. And, after much soul searching, I bred Grindle. She is VERY young, but if she does not take this Spring, or has a bad experience with her litter, she will be much more mature this Fall and will kindle well then. She seemed ready, and weighs 9 pounds already, so is very close to her full adult weight. I am feeding her carefully, for she is still growing and needs lots of extra calories.
At the end of the day, I very much like to breed in March, April and May and then again in September, October and November, although the heat of the late Summer can interrupt the bucks' abilities. I plan to be home for a full week before and 3 weeks after the bunnies are born, to keep an eye on things. Sometimes my teaching schedule interferes with breeding season and I have to rearrange my plans accordingly.