Microsoft word - timing ovulation and mating in the bitch.doc
Timing ovulation and mating in the bitch by Dr Michael Bell
The period in which a natural mating yields maximal conception rates spans for up to seven days in dogs. Hence in many dogs one or more matings during behavioural estrus (i.e. the time the bitch is interested in the dog) will result in pregnancy. However to achieve the highest conception rates and litter sizes it is best to mate 2-4 days after ovulation. Unfortunately the day of ovulation varies between bitches, in most cases ovulation occurs two days after the onset of proestrus (i.e. normally 12 days from when pre-season commences), but this period can vary from 7 – 22 days after the onset of proestrus. Hence predicting the time of ovulation can greatly aid in managing a mating. For managed matings determining the day of ovulation is important in the following circumstances:
where artificial insemination is used (with fresh, chilled or frozen semen) and the cost of each insemination is high and or timing is critical
where the bitch concerned has a history of failing to stand for the stud dog, a history of failing to conceive, a history of small litter sizes, or where there is a need to inseminate her with poor quality semen.
The use of natural matings that are difficult or expensive so that there is a high chance of the bitch conceiving with one or a few matings.
Travelling with bitches after the luteinizing hormone (LH) serge to avoid a fall in LH that can occur during the stress of travelling.
Various methods have been used to predict ovulation. The most common of these are as follows:
Progesterone assay Measuring the concentration of serum progesterone during late proestrus and estrus allows us to predict the optimum breeding time for a bitch. The bitch is unique amongst domestic animals in that the progesterone level begins to rise 2-3 days before ovulation. At the time of ovulation serum progesterone levels reach 15-25. Hence by measuring the progesterone level during proestrus or estrus we can predict the best time to mate a bitch. The best time to mate, if only one insemination is to occur is two days after ovulation (i.e. two days after the progesterone level reaches 15-25).
Luteinizing hormone assays (not commonly used in Australia) Determining the time of LH surge is helpful in predicting the time of ovulation, egg maturation and fustigation because ovulation normally occurs 2-3 days after the LH surge, and egg maturation and fustigation occurs 4-6 days after the LH surge. Unlike progesterone assays which steadily increase during estrus, the LH surge is often only increased for 24 hours, hence a single sample obtained on any day through estrus may not provide information on whether or not the LH surge has occurred.
Increasing levels of estrogen during proestrus stimulate the growth of the cells lining the vagina from a few cell layers of thickness during anestrus (i.e. when not in season) to 20-30 layers at the end of proestrus. As the lining thickens increased numbers of surface cells slough into the vaginal fluid. The change in the percentage of surface cells in a vaginal smear can be used to monitor the progression of proestrus and estrus and can thus be used to predict the fertile period of the bitch. Vaginal smears provide useful information on whether estrus is progressing normally and if the bitch is still in her fertile period when used along with hormone assays. Due to concentrations of progesterone varying among bitches, using progesterone levels only can occasionally lead to erenous predictions of optimum breeding times, but in addition to progesterone assays surface cells predominately seen in a vaginal smear are non-cornified the bitch is beyond the time of ovulation and optimal fertilization and has already reached diestrus (i.e. too late to mate). Identifying the onset of diestrus with vaginal smears can be a very useful tool because it enables us to determine if breedings have occurred at the appropriate times. This onset of diestrus can be done by evaluating daily vaginal smears. Identifying this onset of diestrus also allows us to predict the time of whelping with greater accuracy then using breeding dates alone.
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