Proestrus: Not many signs are seen in the cat for this stage. The female is attractive to the male, but unwilling to mate. Length: 1-2 days.
Estrus: This is when the female cat is receptive to the male. External signs such as a swollen vulva or bloody discharge, are not as obvious in the cat as they are in the dog. The main signs seen are behavioral -- loud vocalizing, rolling on the floor, elevating the hindquarters and possibly a decrease in appetite. Many people have confused the signs of the feline estrus phase as signs of being in pain. Length: 3-14 days (average of one week). If the female is not mated, she may go back into heat within several days.
Interestrus:The period between estrus cycles if the female isn't bred. Length: 2-3 weeks.
Metestrus (or Diestrus): period after estrus or mating. Length: 30-40 days. If pregnant, pregnancy lasts on average 60-64 days in the cat.
Anestrus: period of inactivity (sexual and hormonal) between estrus phases. Length: 2-3 months.
Some general "rules of thumb" for feline estrus:
- The first estrus cycle usually occurs by age 6-12 months; for some cats as early as four months of age, for others not until age 12 months or so.
- Cats are considered to be seasonal breeders; most often showing signs of mating behavior in the spring and fall.
- Cats are induced ovulators, meaning that they only ovulate (release an egg from the ovary) if mated.
- If not mated (no ovulation), the estrus phase of the cycle will return in 1 - 3 weeks.
- Multiple matings produce more ovulations; more than one male can be the sire of a litter.
- Cats can get pregnant during their first heat cycle, but this is not advisable as a 6-month old cat is not yet fully grown/mature, and complications for the mother and the kittens are more likely.
For cats that will be pets, it is recommended to spay them before the first heat, eliminating the risk of accidental pregnancy and reproductive diseases later on in life. Cats may be spayed while in heat (or pregnant), but there is additional risk due to the engorged vessels and tissue of the reproductive tract -- a higher chance of bleeding during surgery or other complications. The cost of surgery while in heat or pregnant is often higher as well.