rabbits don't really have a "heat" like dogs or cats do. they are induced ovulators, meaning they won't release eggs until they are bred, and can generally be bred year-round because of this, provided they have enough sunlight and it's not too hot.
i have read some articles that state that a doe rabbit does have a 'cycle' of sorts, though it isn't a true heat. she will be more or less receptive at different times of the week - i think the time was around every four days she has a couple says where she is more receptive to a buck than normal. so if she doesn't lift today, try again in a couple of days. checking her vent can also be a decent way to see if she's receptive. if her vulva is pale and thin, she likely won't breed. a swollen, reddish or purple vulva means she's more likely to be receptive.
there's also a few more tricks to get does in the mood that have been used with varying levels of success:
- putting a few capfuls of apple cider vinegar in her water for about a week, then putting her back in with the buck. the vinegar is really good for them in general, and helps boost their health, and healthy rabbits want to breed.
- adding a handful of black-oil sunflower seeds to her food. these are rich in fat and vitamins, and again, healthy rabbits want to breed.
- spinach is another thing that is commonly given to does before breeding as it is rich in vitamins.
- try breeding early in the morning or late in the afternoon. these are the normal times that rabbits are naturally active, and the cooler temperatures can make them frisky.
- try breeding in a pen on the ground. something about the extra space and grass on their feet gets them in a good mood
- swap the doe and the buck's cage for a day. being surrounded by his scent can sometimes get stubborn does to lift. i usually will give them a full day + night in each others' cages before putting her back in with him the next morning.
- make sure she's old enough. you didn't mention if your rabbits are new or had been bred before. larger breed rabbits generally do not begin breeding until they're about 5 or 6 months old. younger rabbits can begin younger, around 4 months. if your rabbits are fairly young, she just may not have hit puberty yet. when my does start getting around that age i start checking their vents a couple times a week. when they get colour, they're usually ready.
- make sure she isn't already pregnant! if an of-age doe continuously refuses to breed for more than a week or so, she may already be pregnant and you didn't know it. she may also be ill, so keep an eye out for signs of sickness like lethargy, poopy butt, runny eyes/nose/etc.
hopefully one of these works! unfortunately they don't always breed like rabbits
