Hormonal usage in canine theriogenology (Proceedings)


Bitches with the history of subfertility or infertility should be examined for pregnancy at 25 days following the last breeding using ultrasonographic examination or palpation depending upon the animal and the examiner.

Failure of corpus luteum formation or function

Bitches with the history of subfertility or infertility should be examined for pregnancy at 25 days following the last breeding using ultrasonographic examination or palpation depending upon the animal and the examiner. Ultrasonographic examination is superior in that the owner also can visualize the fetuses. Serum progesterone concentrations should be determined in bitches that are nonpregnant or in pregnant ones when there is reason to believe fetal resorption or abortion has occurred in the past with no other apparent reason.

Progesterone concentrations in nonpregnant bitches below 5 ng/ml indicate possible luteolysis has occurred. Concentrations less than 1 ng/ml indicate ovulation did not occur or very early luteolysis did occur. In bitches where premature luteolysis is suspected or differentiation between the two conditions is necessary, serial progesterone concentrations at 5 to 7 day intervals through day 25 or further into gestation is recommended. Ovulation failure is an unlikely cause of lowered progesterone if estrous behavior, luteinizing hormone concentrations, vaginal cytology and/or vulvar discharge and swelling were normal. Clients must always be advised before starting progesterone supplementation, that progesterone supplementation in bitches during pregnancy may induce masculinization of canine fetuses.

Estrus suppression

Ovaban is not indicated or recommended for use in breeding bitches. It is a progestational compound and as such does increase the possibility of pyometra or cystic endometrial hyperplasia. Mibolerone is an androgenic hormone used for estrus suppression. It has the potential, as do all androgenic steroids of inducing hepatotoxic lesions but this has not been reported in the canine with recommended use. Its primary side effects include increased lacrimation in toy breeds and clitoral hyperplasia with prolonged usage. Although not approved for use in breeding bitches. the author routinely uses it for suppression of estrus for 6 to 10 months or at times longer, and had a non-breeding animal on medication for 12 years with no adverse side effects.

Desorelin implants down regulate the production of FSH from the pituitary. Synthetic GnRH preparations given at high doses cause a decreased production of FSH.

Cystic ovaries

Cystic ovaries are primarily demonstrated by prolonged proestrus and/or estrus. Signs of both occurring repeatedly multiple times during the same estrus are possible, It may be called a split heat or cystic ovarian disease but it is the same condition. Based upon information available in other species, the prolongation of a mature oocyte within the follicle reduces the probability the oocyte will be fertile and that ovulation will be normal. For this reason and because this condition can persist for 6 to 8 weeks if untreated, the author prefers to treat accordingly with human chorionic gonadotropin as soon as possible and not breed the bitch. The success of this therapy is extremely high with over 90% of the animals responding to a single treatment. The bitches cease the proestrus or estrus within 5 to 10 days. Recommended dosage is 500 to 1000 units administered intra-muscularly. GnRH has also been used at a dosage of 50 ug administered intramuscularly. Since the proestrus and estrus were prolonged it is advisable to always examine these animals at 25 to 35 days following treatment for the possible development of pyometra. The treatment does not cause the pyometra, the prolonged exposure to the estrogen predisposes to the condition.

Uterine subinvolution (subinvolution of placental sites)

The cause of uterine subinvolution is unknown. It is known that the endometrial vessels do not thrombose and occlude as normally occurs following parturition. The signs include a bloody discharge for 4 days to 16 weeks. There are no systemic signs associated with this condition even if permitted to persist for months. Spherical uterine enlargements may be seen or palpated in the uterine horns at the placental sites. Vaginal cytology is diagnostic for this condition since the sample will reveal numerous RBC's with no WBC's in a bitch that has the history of whelping in the recent past. Considerations to be made with uterine subinvolution include: no elevated progesterone, no infection present (uterine or systemic), no dystocias involved, no problems with the fetuses or neonates, and no effect on future fertility.

The differentials include any condition involving the lumen of the reproductive tract and a discharge from the vulva such as metritis, vaginitis, vaginal neoplasia, or vaginal or vestibular trauma. The diagnosis is made by the history plus the vaginal cytology. No other diagnostic aids are necessary. The treatment of choice for a non-breeder is ovariohysterectomy. For breeding bitches the following treatments have been used. Ergonovine is the oldest of the treatments but is not recommended currently because prostaglandin F2alpha has been found to be superior. Oxytocin is of no value because of the time frame when this condition is diagnosed is when the uterus is no longer sensitive to this hormone.


The first consideration when selecting a treatment for mismating is to determine if the bitch is to be used for breeding. If not, an ovariohysterectomy is the treatment of choice. This is best accomplished with least increased risk to the bitch if performed within the first 4 weeks following mismating. This will obviously eliminate future problems with unwanted pregnancies.

When considering treatments and primarily for the owners sake, the vaginal cytology can be examined for the presence of sperm within the first 12 hours following the mismating. If sperm are observed within this time or afterwards then the owner can be advised that a breeding did occur. Many of the bitches presented to our hospital were not observed bred but "ran off" while in heat. If no sperm are observed outside the 12-hour window, no conclusions can be made. Regardless of the presence or absence of sperm, it does not alter the recommendations made to the owner as to how we handle the case.

Estrogens have been used for the termination of unwanted pregnancy for years with some practitioners never having encountered a problem. The author and most theriogenologists do not recommend its usage. If used, the estrogen should be given before the embryo passes into the uterine lumen so as to retard the transport of the embryo by causing contraction of the isthmal sphincter of the oviduct. It also causes a degeneration of the embryo and an alteration of the endometrium and this is generally why a second administration is given. Estradiol cypionate (E.C.P.) has been administered at the dosage of 0.25 to 1 mg per bitch. Diethylstilbestrol given at a dose of 1 mg/lb up to a maximum of 25 mg has been administered once intramuscularly. The recommendation is to administer it immediately after the breeding occurs in order to prevent normal development within the oviduct, and again 7 days later to create an undesirable environment within the uterus in case fertilization and development did occur.

The major disadvantages of the administration of the estrogens include: extension of the length of time the bitch is exhibiting signs of estrus; increased predisposition to pyometra occurring during diestrus; and increased possibility of bone marrow suppression (bone marrow aplastic anemia) that may or may not be reversible and may result in death of the bitch. Diethylstilbestrol appears to be less potent in the production of bone marrow suppression but still has this potential.

Prostaglandin F2alpha is not approved for use in the canine but has been frequently utilized for over 25 years because of its excellent results. My recommendation is to determine if the bitch is pregnant at 25 to 30 days before starting this treatment. If the bitch is nonpregnant, no treatment is necessary. Prostaglandin F2alpha works best when given after day 18 of gestation. Several doses and frequencies of administration have been recommended in the literature. My recommendation is if it is the first time you are using it: give 50 to 100 micrograms/kg SQ in an expanded 5 to 10 ml final volume; then give 100 to 150 micrograms/kg SQ in a 5 to 10 ml final volume; and finally give 250 microgram/kg SQ in a 5 to 10 ml final volume repeated every 12 hours until embryos or fetuses are gone. This may require 5 to 10 days of treatment depending on the day of gestation treatment was started. Further past 30 days the longer the PGF2alpha may have to be given. If you have used PGF2 alpha and are comfortable with it, start at the 250-ug/kg dosage SQ with expanded volume every 12 hours. The side effects include: increased salivation; increased heart rate; increased respiration, increased defecation, increased urination, increased gagging, vomiting, ataxia, and mild depression. These side effects begin approximately 20 minutes following administration and end approximately 20 minutes after initiation. Bitches can be aborted starting treatment at 53 days of gestation using this procedure. The advantages of this treatment is that it is physiologic, there are no long term effects on the bitch, and there are no short or long term effects on reproductive health.


Pyometra is initiated by an interaction of hormonal influences and uterine bacteria. The endometrium physiologically is altered due to repeated exposure to estrogens and progesterone in some bitches. This results in an eventually atypical response to this hormone. There have been no reported differences in the occurrence of pyometra with regard to pregnancy characteristics or between lesions seen in bitches having had a pseudopregnancy and those that did not. Pyometra has been associated with the presence of corpora lutea, cystic corpora lutea, older age of bitch, and the first four weeks following estrus. Death of the bitch can occur if not treated promptly after systemic signs are present.

The predisposing factors to pyometra are: age, cystic endometrial hyperplasia, uterine bacteria, diestrus, estrogen administration and progesterone administration. The progression to a pyometra follows introduction of bacteria into the fluid within the cystic endometrial hyperplastic lumen. Pyometra has been observed to occur only during or immediately after diestrus while progesterone is elevated. One study reported that 75% of dogs with pyometra less than three years of age had been given estradiol cypionate or megestrol acetate within the previous six months.

Uterine cultures of dogs with pyometra contained: E. coli in 66% of the uteri, Klebsiella sp. in 11%, Pseudomonas sp. in 6%, Proteus sp. in 6%, Staphylococcus aureus in 6%, Hemophilus sp. in 4%; and Serratia sp. in 2%. This may justify the need to culture the uterine discharge but will be discussed later.

Antiprogestins is another treatment the for open cervix pyometra. Give Aglepristone (RU534) 10mg/kg SC every 5 days until cured. This can be administered with Cloprostenol 1ug/kg SC (not during feeding) every 5 days for 15 days (if not cured earlier). Clavamox 12/5mg/kg (bid PO) and supportive hydration throughout the protocol can be administered in indicated. Cabergoline is also beneficial for treatment of pyometra since it is an ergot derivative.

Gram negative bacteria release a biologically harmful endotoxin [lipopolysaccharide (LPS)] during the disease process and following the use of bacteriostatic or bacteriocidal antibiotics. Endotoxic substances remain active for up to two weeks in tissue. Normal bitches have circulating LPS concentrations of 0.053 + 0.004 ng/ml. Pyometra bitches have concentrations of LPS ranging from 0.091 to 0.956 ng/ml. The lethal range of concentrations is 0.7 to 1.0 ng/ml. The LPS possesses many undesirable capabilities including: detrimental vasoactive actions and neuroendocrine actions, and a detrimental influence on complement, kinin, and the hemostatic systems.

The vaginal cytology of a bitch with pyometra will have increased numbers of white blood cells and would be indicative of a genital tract abnormality but not specifically uterine disease. Samples should be taken immediately following the obtainment of an anterior vaginal culture using a guarded culture rod. Cultures are most useful for the determination of antibiotic sensitivities for proper selection of antimicrobial agents. Endoscopic examination has been found to be useful in the determination of the origin of vulvar discharges. It also proves useful for differentiation of discharges originating from vaginal or vestibular tumors.

Prostaglandin F2alpha (PGF2alpha) has been very successful in treating pyometra. Currently it appears to be the medication of choice. Although not approved for use in the canine in the United States, it has been widely used for treatment of pyometra in this species. The actions of PGF2alpha which are beneficial to treatment include: contraction of the myometrium and relaxation of the cervix. These two actions aid in physical expulsion of the pyometra fluid from the uterine lumen.

Recommended use of PGF2alpha in animals with pulmonary or cardiovascular disease varies due to the effect of this hormone on these systems. Although no deaths have been directly attributed to the PGF2alpha treatment, caution should be taken when treating animals with these conditions. Side effects to be expected commenced within 20 minutes following PGF2alpha administration include: restlessness, increased respiration, increased lacrimation, increased frequency of defecation, increased frequency of urination, abdominal pain, increased body temperature and vomiting. These side effects usually last for 20 to 30 minutes.

Systemic antibiotics should be administered concurrently with PGF2alpha as 10% of treated bitches reportedly have a positive blood culture. Plasma enriched with anti-lipopolysaccharide (LPS) (endotoxin) immunoglobulins alone or in combination with conventional therapy has been used for treatment of pyometra.

Normal germinal epithelium but poor to no sperm prodcution

Dogs which have had a testicular biopsy and found to have normal germinal epithelium present but producing no to low sperm numbers can be given hormonal therapy in hopes of stimulating spermatogenesis. The success of this therapy is less than half of the animals treated. The following is based on a dog weighing 40 to 90 pounds. PG 600 can be administered at a dose of 2.5 cc SC or IM three times per week for 6 weeks. Human chorionic gonadotropin can be given at a dose of 250 units SQ or IM twice a week for three weeks starting at the 5th week of treatment with re-examination of semen during the last week of treatment. Discontinue treatment if any suspected side effects occur.

Other hormones have been used in the male, however their results are unproven. PGF2alpha increases libido and sperm output. Cystorelin (GnRH) has been used at 3.3 micrograms/kg and has increased sperm numbers. Additionally, GnRH agonists used at 1/1 micrograms/kg is thought to increase the number, motility, viability of normal sperm while decreasing the amount of abnormal sperm. Prolactin inhibitors, such as Cabergoline, only work in males with hyperprolactinemia at 5 micrograms/kg. Nutritional supplementation is also considered, however more research is necessary to prove the efficacy of this therapy.

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