Due to the growing demand for veterinary services in the field of fertility, many veterinarians began to deal more closely with defining of the most appropriate time for mating. In fact, the reproductive failures are for the most part due to an error in choosing the date of the coupling rather than to a male or female infertility.
This concept is even more important nowadays, if we consider that often the females find the male suitable for breeding hundreds or sometimes thousands of kilometers away and that sometimes they have the possibility to carry out only one mating.
The old scheme in which it is described that the female is fertilizable on the 12th -13th day from the beginning of the heat, often turns out to be inaccurate as well as relying on the female’s estrous behavior or the appearance changes of vaginal discharge.
The time of ovulation varies from bitch to bitch.
The success of the coupling depends on recognizing the moment of ovulation.
The vet who deals with breeding problems has two methods to determine the ovulatory day of the female:
Vaginal smears are easy to perform and inexpensive. The examination consists in the observation of slide under a microscope, on which the cells of the vaginal wall are swiped with a tampon and in the evaluation of their corneification.
The estral cycles in female consist of four periods:
OESTRUS: begins the first day when the female accepts the male and ends the first day she refuses him. On average it lasts 9 days (3 days – 21 days). The female accepts the male, arches the back, diverts the tail to the side and remains still when the male tries to mount it. Losses progressively decrease and go from red to pink. Ovulation occurs during estrus but with the pathological examination (slide) the moment can only be assumed. Mycologically the red blood cells diminish or disappear and the epithelial cells become corneified and lose the nucleus.
Only cornified epithelial cells are visible at the apex of the estrous phase.
But the appearance of the maximum corneification of the vaginal cells varies from one bitch to the other and can have an oscillation even a few days compared to ovulation. Therefore, the cytological examination of vaginal epithelium alone is not an accurate index of the ovulation of the bitch but it remains an important method to evaluate the progression of the estrous cycle and to determine the most suitable moment to start the measurement of serum progesterone.
DIESTRUS: begins the first day when the female refuses the male again and ends after about 9 weeks. At this point some bitches manifest the so-called hysterical or imaginary (false) pregnancy.
ANESTRUS: it’s the period of pause between one heat and the other.
If the phytocithological smear (slide) shows us the approach to the fertile period in the bitch, allowing us not to make progesterone evaluations too early or too late, the evaluation of plasma progesterone allows us to identify the exact period in which to perform the mating. It is a very simple test and consists in evaluating the progesterone dosage (in nanograms -ng) contained in a blood sample of the affected female.
Ovulation occurs when progesterone reaches a level of 7-8 nanograms / ml. Once the ovulatory moment has been established, it is necessary to wait for the mating 36-48 hours, that the eggs pass from the ovaries to the Fallopian tubes (where the meeting with the spermatozoa takes place) and undergo the first meiotic division and therefore be fertilizable.
The increase of progesterone is not regular.
Its baseline value is 0.5 ng / ml.
It is therefore advisable to do at least two or more evaluations of the progesterone to identify the exact moment of ovulation.
Let’s take a few examples:
The determination of the blood levels of progesterone is a fundamental help also for the determination of the time of delivery.
The best method to establish the date of delivery is to calculate 63 days (+/- 1) from the date of ovulation (see above).
This date can also be confirmed by the measurements of progesterone carried out in the last days of pregnancy: in the days preceding delivery there is a drastic decrease in the levels of blood progesterone which decreases to levels of> 2 ng / ml few hours before delivery.
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