Once a rabbit dies, its body will go through a series of changes as it decomposes. The time it takes for a rabbit to go stiff depends on a number of factors, including the temperature, the humidity, and the size of the rabbit. In general, however, most rabbits will be stiff within 24 to 48 hours after death.
The first sign that a rabbit has died is usually its lack of movement. Once a rabbit stops moving, its body begins to cool down. As the body cools, the blood vessels in the extremities contract, which causes the limbs to become pale and limp. The skin may also start to sag and wrinkle as the muscles lose their tone.
As decomposition progresses, bacteria inside the rabbit’s gut begin to break down its internal organs. This, in turn, causes a buildup of methane gas inside the carcass. Meanwhile, fungi and maggots may start to grow on the skin within 24 hours after death. The hair will fall out as the skin breaks open and releases fluids. The carcass also begins to swell up because of gases building up inside it.
Within 48 hours after death, the muscles will be completely stiff (rigor mortis). At this point, you can be fairly certain that there is no chance your rabbit might still be alive if you were to check for signs of life like breathing or movement.
If it is still warm outside, your rabbit’s body may start to rot and decay quickly. If it is cold, however, the process of decomposition will be slowed down significantly. Under certain conditions, your rabbit’s body may even begin to mummify. If this occurs, you can dry up its remains with heat or bury them in moist soil until they become desiccated. Your rabbit’s body might not be entirely intact when you find it again after three weeks of burial, but at least most parts of the carcass should remain whole for easy handling during disposal.