Female dogs will go into "season" on the average of every 7-8 months
although the range can be every 5-14 months. You must know what your
own dog's pattern is. In the case of a young dog, the first heat can be
from 6-14 months of age.
The easiest method to tell if she is in heat is with a male dog. They
will take interest, try to lick, or often mount the females even in
early "heat". You may see this behavior as early as 2 weeks before heat
between 2 females. This can be an early clue that a heat cycle is
close. If the males are not available, there are physical signs to look
for. These are:
Swelling of the vulva. Normal anoestrus vulva is small. The vulva begins to swell early in the course of a heat cycle and continues to a maximum in about a week. The inside lips of the vulva are pink and firm. Some bitches have more swelling than others. As estrus progresses, the vulva becomes softer and more flexible and as they go out of heat, you will see a decrease in the size of the vulva. As this happens, there may be wrinkles in the vulva and the color of the membranes turns from pink to almost a gray color. Bitch's that have had puppies will have a larger normal non-heat vulva but it will still enlarge when they are in heat. YOU MUST KNOW YOUR DOG!
Vaginal Discharge. About the time the vulva begins to swell, a blood-tinged discharge begins often turning to bright blood drops over the course of a week then decreases in color up to the time of receptivity. Some bitches will discharge blood throughout the entire cycle. There is a lot of variability in that some females will be receptive at 5-25 days into the cycle. You must know your dog to know this. You can check for color of the discharge with a sterile Q-tip swabbed into the vulva an inch or two.
Response of the vulva to touch. The vulva and adjacent tissue will become sensitive to touch during estrus and can be used as a sign of readiness to breed. Early in the cycle, if the skin above the vulva and below the anus is touched, there will probably be no response. As the cycle progresses, this area will become responsive, and when stimulated during estrus, the bitch will flag her tail and the vulva area will be elevated to the position needed during mating.
If there is any question about a heat cycle, sequential vaginal
smears taken and interpreted by a qualified professional along with
physical examination the day before the hunt test should determine if
your dog is in heat or starting a heat cycle. If your female is in any
of the stages of heat, they are not allowed on the hunt grounds.