When the chosen stud is not always available in the breeding facility, and since it is customary that the bitch be brought to the male for mating, it is important to choose just the right moment, in order to maximize the chance of fertilization and thereby avoid unnecessary travel and expense. Ideally, mating or insemination should occur in the 48 hours after ova are released, in order to increase the chance that the most fertile ova and spermatozoa will reach the "meeting place" (the oviducts). Ova remain fertile for two days after maturation (some breeds, such as the Welsh Corgi, seem to remain fertile for more than 4 days); thus the possibility of superfecundation by two different sires. Given the short survival time of spermatozoa, breeders do have a certain safety buffer.
To determine the ovulation period of a bitch in heat, the breeder can combine several methods of varying and complementary accuracy.
-Mating conducted approximately twelve days after blood is first discharged and repeated two days later is still a practical formula for the breeder. Approximately 20% of bitches do not ovulate during this period; as they do not conceive, or deliver only a few puppies, the loss of revenue for the breeder is clear.
-The lightening of vulvar discharge following the discharge of blood generally indicates the end of proestrus, but it is not a reliable sign of ovulation. Some bitches, such as Chow Chows, may show some blood discharge until the end of estrus.
-Accepting the male or teaser dog and Liebenberger's sign (a lateral change in tail carriage) are not signs of ovulation, either. For example, some Doberman bitches were reported to allow mounting from the very beginning of proestrus, although they did ovulate 30 days later in the most extreme cases! Many bitches allow mating during:
-alse heats before whelping,
-urinary infections,
-estrogen secretions by follicular cysts which lead to nymphomania.
-The resistivity of vaginal mucus generally decreases just after ovulation, indicating the end of the period of estrogenic impregnation and, consequently, the rapid renewal of vaginal cells. Measuring this factor provides a diagnostic tool which unfortunately comes too late for breeding purposes, since anticipating imminent ovulation is more useful than knowing it has just occurred. Furthermore, as the cost of a galvanometer and the risks of infections among bitches associated with this method are significant, this technique falls into disuse in canine breeding.
-Reagent strips revealing changes of the rate of glucose in the vaginal mucus are difficult to introduce far enough into the vagina to avoid contamination by the urine. The results are usually imprecise (since the color change is seen within the three days preceding or following ovulation), and therefore not very reliable.
-By monitoring the color of vaginal smears, breeders can correlate any change in the appearance of the vaginal cells with hormonal variations, particularly with regard to estrogen.
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