Bitches can go into their first heat as early as five months, and as late as 18 months. Usually, the first heat is between seven and eleven months. Most females who don’t have an observable first heat have had either a ‘silent heat’ (not showing physical signs, but the males will know) or they happen to keep themselves very clean.

Generally, the first heat is when a bitch is about 85% of her adult size. Some dogs grow more quickly, some more slowly, and therefore this stage can occur at different times for females in the same litter.

Every female is a bit different, but here are some general guidelines-

The first sign of a heat is emotional change, maybe more clingy, wanting attention or interested in playing. This is usually not noticed.

Bleeding will begin to show on what we call Day 1. She is not ready to breed yet. During the first days of bleeding, the cells within the walls of the vagina are being ‘cornified’ – a term that means they are changing shape and toughening up in preparation for breeding. She will not want the attention of a male at this time. Likely, she will become annoyed with other females, grouchy.

Ovulation occurs as early as Day 5 or as late as Day 20. Most frequently near Day 10.

Some vets track progesterone levels if they want to be sure which day a bitch is ovulating as the progesterone will suddenly increase dramatically when ovulation occurs. There is no exact level of progesterone, it is individual – but all suddenly increase at ovulation.

The easy way to see when a bitch ovulates is that she will stop bleeding and the discharge changes to a tea-color liquid. She will begin to turn her tail to the side when a male is smelling her, and maybe even if someone she knows scratches her back. Some females are very picky about choosing a male, and others are not choosy at all.

Puppies are born 63 days after ovulation (O-Day 1). Large litters or problematic pregnancies may be a day early, but 99% of the time, puppies are born 63 days from ovulation.

However, due date is not necessarily 63 days after mating.

Sperm can live inside a female for at least five days (unless it is frozen or chilled – this is for natural breedings) and a female will be willing to breed for three – five days. The eggs are released on Day 1 of ovulation (O-Day 1), but are immature and cannot be penetrated by the sperm. Same for O-Day 2. At the end of O-Day 3, the sperm can begin to penetrate the egg. O-Day four, all the eggs are mature and can be fertilized. O-Day 5, the eggs are ripe and some are beginning to die, but fertilization can still occur and result in a smaller litter.

So, eggs are fertilized 3-5 days after ovulation/ 61-58 days before puppies are born. But puppies are always born 63 days after ovulation.

Natural breedings can be successful up to five days before the third day of ovulation/egg maturation. Because sperm can live five days, this adds two extra days to the possible due date from breeding. If the female is bred two days before O-Day 1, the puppies are born 63 days after ovulation, but egg penetration by the sperm is three days later – your puppies will be born 65 days after breeding. This almost never happens with gamprs, as females are very tough and usually keep the males away until they are truly ready.

At the other end of the spectrum, successful breedings have been known to occur as late as O-Day 6. Not common, but possible. As it is the sixth day from ovulation, this gives a possible due date of (63-6) day 57 after breeding.

Most litters are born 59-61 days after breeding.

An easy way to calculate is to give three days on either side of the day of the month, two months later than the date of the breeding – for instance, if your bitch was bred May 15, calculate that the most likely due date is July 15, plus or minus three days.

Some bitches will have a false pregnancy, showing signs of milk or slight swelling of the belly. By the end of four weeks, you should be able to visibly tell if a bitch is truly pregnant.