THE bitch is described as being monoestrus, which means that a long period of anoestrus occurs between successive periods of oestrus, whether she becomes pregnant or not. Correct monitoring and timing of the cycle is, therefore, essential if a fertile mating is to be achieved, since the next opportunity will not occur for some time. An important consideration when attempting to achieve a successful mating is the variation which occurs both between bitches and between cycles in the same bitch in the timing of ovulation in relation to the onset of proestrus. Despite this, many breeders continue to time matings using a standard number of days from the start of vulval bleeding (onset of proestrus). Bitches are, therefore, often mated at an unsuitable time, resulting in an apparent, and usually avoidable, infertility. Correct timing relies on the detection of physiological changes that occur between the onset of proestrus and oestrus. As discussed in this article, there are several different techniques which may be employed to assess the optimal time for mating, including measurement of plasma hormone concentrations, examination of exfoliated vaginal cells, and vaginal endoscopy.

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