Timing and Frequency - Most bitches have their first 'season' before they are twelve months old, although some can be as late two years, although this is irregular. Having a 'season' is also commonly called 'in heat'. The subsequent frequency of the 'heat' cycle depends on the breed, but is usually every five to ten months.
Coming into season - There are a few tell tale signs of when your bitch is about to come into season. Not all bitches show all the signs, but usually some are present.
The most obvious sign is spots of blood around the vulva, in this case you need to make a note of the date and start making arrangements for the mating.
Knowing when your bitch is ready - There are two stages of a season, pro-oestrus and oestrus, the length of each stage varies according to the breed, but it's usually around eight to ten days.
During the pro-oestrus stage the bitch will release a blood stained discharge and her vulva will be enlarged, she will more than likely reject advances from a male dog at this time.
During the oestrus stage the vulva will swell further and the discharge will be pale yellow in colour. It's during this second stage that the bitch will welcome the male dog. The most fertile period is two days after the onset of the second stage. This is the period of ovulation.
If you are unsure about the time of ovulation your vet will be able to carry out a test on your bitch. This may also be advisable if you have had an unsuccessful mating in the past.