The leading cause of an unsuccessful mating is improper timing. Most dog owners attempt to breed on the 10th to the 14th day of the heat cycle. Recent advances in the understanding of the reproductive cycle of the female dog indicate that ovulation cannot be accurately predicted just by counting the days of the heat cycle. You may miss the early signs of heat, or your dog may show very little evidence of them.
Also ovulation may occur several days after the female is in standing heat instead of the first day. Furthermore, when the eggs have been shed they must mature for 72 hours before they can combine with the sperm. Fortunately, nature provides a safety factor in that sperm are able to survive for up to 7 days in the female reproductive system.
Phases of Estrous Cycle
Canine heat cycles are divided into four separate phases. Each phase has specific outward signs associated with it, as well as attitude, hormonal, and other internal changes. The heat period usually comes every 6 to 8 months. However, some females may go into heat every 4 months and others only once a year depending of hereditary tendencies and emotional states.
Proestrus is the first phase of the estrous cycle. All the females reproductive tissues thicken, her vulva swells, and visible genitalia becomes reddened. Bloody vaginal discharges are produced and a female spends a considerable time licking her genitalia. she may act nervous and her appetite is reduced. IN early proestrus some females can be snappy toward other animals. Proestrus lasts from 2 to 27 days, more typically 7 to 10 days. Some females have a very light pinkish to yellow discharge early in proestrus. If you are not sure whether your female is going into heat, wipe a Kleenex across her vulva. If you see a pinkish color on the kleenex, she is in early heat.
Estrus is the second phase of the estrous cycle. It corresponds to the stage often referred as "standing heat". It lasts from 6 to 10 days, but on average for 9 days. It is during estrus that a female will mate with a male. A vaginal discharge normally persists during the estrus period and the vulva becomes soft. Ovulation is the expulsion of the eggs from a female's ovaries and its timing is very important with relationship to fertilization of the eggs (ova).
Metestrus is the third phase of the estrous cycle. It begins when a female refuses to stand for the male and lasts through the period of uterine repair (about 60 to 150 days). After a female has gone into heat once, her breasts and vulva will remain slightly larger than before.
Anestrus is the fourth phase of the estrous cycle. This is a period of reproductive rest. It lasts 100 to 150 days.
There are reports of females being bred as early as the 4th day and as late as 21st day of the mating cycle - and yet conceiving a litter. Practically speaking, a certain amount of trial and error is necessary. Accordingly, many veterinarians recommend that females be bred three times; on the 2nd, 4th and 6th day of standing heat. An important indicator is the deportment of the female. If she plays coyly, if she flags, if she presents her parts and stands firm - these all are signs that she is ready to be bred. Other signs are softening of the vulva and lightening of the discharge. Vaginal smears taken by your veterinarian, or a sugar test of the cervical secretions, may be helpful in determining the best mating-time. An experienced stud dog will make his own investigations. A knowledgeable one ignores the female until the moment is right.