"Maximizing Conception Rate"
Since 1981 when the American Kennel Club recognized litters conceived from frozen semen, and subsequently, litters produced from fresh-chilled semen, veterinarians are being asked more frequently to assist clients with maximizing bitch conception rates. One of the great rewards in veterinary medicine is the feeling of gratification when successful conception in the bitch is achieved.
OVULATION IN THE BITCH
The bitch is unique when compared to other domestic animals. The ova are ovulated in a progesterone "bath" as opposed to the estrogen environment of other species. The uterus is not easily accessible due to the cervix being difficult to reach, small in diameter, and irregularly shaped.
The bitch ovulates an immature egg that requires a further meiotic division before fertilization can occur. All this process takes place in an estrous cycle averaging 21 days, of which the fertile period is approximately 72 hours.
Ovulation timing in the bitch has been attempted using many methods including
Flagging, softness of the vulva, and color of discharge historically have been used to determine the proper time to successfully breed a bitch. The fact that fresh semen lasts for a number of days in the bitch allows for "rough guesses" of ovulation to be successful in achieving conception. Multiple breedings also cover a wide range of time, making conception likely.
The recent popularity of fresh-cooled extended semen, frozen semen, and limited availability of desired males has made a more specific method of ovulation mandatory.
The use of estrogen for anticipating the ovulatory timing of the bitch is not reliable. The most frequently used method of estrogen monitoring has been through the use of vaginal smearing. By taking a cotton swab and sampling the cells lining the vaginal tract, one can gauge the development of the ovarian follicles.
As the estrogen level rises, the vaginal wall thickens. As the serial samples are taken, one compares the cellular hydration, cytoplasmic/nuclei ratio, and the staining of the chromatic material. As the estrogen level continues to rise, the vaginal wall will reach a 25-30 cell thickness. The cells dehydrate and become "cornified."
The dehydration of the vaginal epithelial cells does not, however, reach a peak but rather stays in a greater than 80% cornified state for a period of 6-10 days. This does not equate with ovulation timing or indicate that the ovulation has actually occurred (D)ue to the uniqueness of the bitchs ovulatory process, estrogen is not an acceptable nor a consistent method of timing the bitch's breeding pattern.
Lutenizing hormone (LH) spike.
Lutenizing hormone from the pituitary gland triggers the release of the ova from the follicles. The release of the LH occurs for a 12- to 24-hour period. Urinary testing for LH was unsuccessful due to the necessity of collecting the first morning urine from the bitch and the fact that the LH is metabolized into different fractions, some were detectable in the urine by commercial testing, while other fractions were not.
Serum testing for LH has been used successful to anticipate the release of the ova. An initial rise of progesterone from the ovarian follicle triggers the pituitary to release the LH. The short duration of the LH in the bloodstream requires daily testing, which can be both time consuming, as well as uncomfortable for the patient. Lutenizing hormone is species specific and levels cannot be confirmed by sending the serum to an outside lab. No laboratory in the United States is currently running canine LH on a commercial basis.
The release of progesterone from the ovary and its subsequent rise to an average of 2 to 3 ng signals LH release from the pituitary gland and denotes the start of the ovulatory process. The rise of progesterone to greater than 5 ng (5 to 8 ng) indicates that ovulation has occurred. Once the ovulation day has been confirmed, insemination timing can be planned depending on the anticipated life of the semen being used.
The bitch needs to be tested every 48-72 hours to anticipate the prime breeding time. Progesterone rises and continues to stay elevated for approximately two months in the bitch, whether or not she is pregnant.
The normal time interval between LH release and ovulation is 48 hours. Cortisol release needs to be a concern when doing progesterone testing as stressed bitches may have a delayed period between a rise of 2-3ng and the time that the progesterone rises greater than 5 ng. It is essential, when using progesterone testing, to confirm that the bitch has risen above 5 ng and has indeed ovulated.
Reported problems have made the in-clinic use of progesterone Elisa test of questionable value. Hopefully these problems can be corrected and these valuable tests can be returned to the veterinary laboratory.
METHODS OF BREEDING
If the male is proven, local, and available, a natural breeding is the preferred method. Progesterone testing is still necessary to confirm that the breeding corresponds with ovulation.
Vaginal Artificial Insemination
If timing is correct, but a natural breeding is not possible nor desired, a vaginal insemination will enable the semen to be deposited at the external cervical opening. This method can also be applicable when a natural breeding can be a risk for disease, injury to the dogs, or an inconvenience to the owner.
The drawback to a vaginal insemination is that the semen is deposited in the vagina and must be properly positioned for it to be drawn into the uterus so that the sperm cells can swim to the fallopian tubes (around the ovaries) where conception occurs. When proper timing of the estrous cycle is performed and proper semen handling and delivery is accomplished, conception rates should rival those of natural breedings. Delivery technique problems, such as improper placement of the insemination rod, improper semen placement, or semen damaged due to mishandling, unfortunately have convinced many dog breeders and veterinarians that artificial inseminations should be only used as a last ditch measure .
INTRAUTERINE DEPOSITION OF SEMEN
A technique for surgical insemination in the bitch was first described in 1974. The intrauterine deposition was first used to increase poor conception rates in the use of canine frozen semen. Since that time, deposition of semen into the uterus has become a routine technique used in numerous situations encountered in canine reproductive medicine, resulting in dramatically improved conception rates. Situations where this can be helpful include the following:
Frozen semen. Due to the lack of spermatozoa energy, buffer chemical makeup, or cervical resistance, the conception rates from cryo-preserved canine semen have been historically low when used with a vaginal insemination. Deposition into the uterine lumen has resulted in conception rates equal to those from natural breeding
Fresh cooled extended semen. Shipping semen rather than shipping the bitch has become common. Due to shipment time and spermatozoa energy depletion, numerous clients have chosen intrauterine semen insemination for their bitches, in hopes of increasing conception rates.
Bitches with suspected uterine or ovarian disease. The ability to assess uterine and ovarian health at breeding time is advantageous to clinicians presented with bitches with histories of reproductive failure. This can be accomplished doing a surgical insemination .
Males with lowered or compromised spermatozoa rates. Little work has been done in the canine to definitively define minimum semen parameters necessary for conception. By directly depositing the semen into the uterus and bypassing the cervix and vaginal vault, conception can be achieved with lesser sperm numbers and lesser overall semen quality.
(The full-text article is available from the Health Committee.)