Factors Leading To Infertility In Bitches
There are many factors that may cause infertility in a bitch. Timely diagnostic work is often required to identify the primary problem before treatment.
Persistent Anoestrous (Lack of Cycling)
A bitch is considered as having persistent anoestrous when she fails to cycle by 24 months of age. Cause of anoestrous may be due to the following:
a. Previous desexing: Most puppies are now desexed as early as 7 weeks of age. Some owners may be unaware that the bitch purchased has been previously desexed.
b. Silent heat: This occurs in bitches where the ovary is active but swelling of vulva, vulval bleeding and attraction of male dogs are absent. Bitches that are thought to have silent heat can be diagnosed by taking monthly progesterone assays or conducting weekly vaginal smear investigations. If the progesterone level rises above 2 nmol/ml or vaginal smears show an increasing number of cornified cells the bitch is diagnosed to have a silent oestrous.
c. Sexual abnormalities: A dog may appear as a female but has abnormal chromosomes (i.e. genetic materials) or have male gonads but with female external genitals (male pseudohermaphrodite). Such dogs can be determined via visual inspection of abnormal external genitals, biopsy of each gonadal tissue, measurement of hormone levels or assessment of karyotype.
d. Drug induced anoestrous: Bitches receiving androgens (e.g. anabolic steroids) or progesterone may not cycle. In addition, bitches on medication for health or behavioural problems can have interference to their oestrous cycles, while bitches receiving corticosteroid (i.e. cortisone) often have reduced fertility.
e. Hypothyroidism: It is the most common hormonal disorder of dogs and in some cases cause infertility. Noticeable reproductive signs have been reported in some bitches that are hypothyroid. Such signs include anoestrous, prolonged or irregular intervals between oestrous cycles, reduced intensity or duration of oestrous cycles, increased incidents of spontaneous abortion, stillbirths, mummified puppies and small size puppies. Non-reproductive signs also appear in some affected bitches which include lethargy, obesity, hair loss and slow hair regrowth.
A tentative diagnosis of low thyroid hormone can be made based on medical history and clinical signs, but a definitive diagnosis requires a series of thyroid blood tests.
L-thyrosine is required to be administered twice daily by mouth to supplement the low body thyroid level when hypothyroidism level is confirmed. The blood thyroid level is retested 4 to 6 weeks later to ensure the level has risen satisfactorily, and routinely rechecked each 6 months. The bitch should resume normal cycle within 4 to 6 weeks of treatment if the problem of anoestrous is due to low thyroid levels.
f. Systemic disease: Bitches with diseases such as kidney failure or cancer are often less likely to cycle than normal bitches. Full blood and urine tests must be performed in bitches with primary anoestrous to ensure the bitch in question is not affected by systemic disease.
Dogs suffering from Cushing's disease may have a persistent anoestrous due to elevated blood cortisol level causing reduction in Lutenizing hormone (a reproduction hormone) production and release.
g. Ovarian cycts: Ovarian luteal cysts may produce progesterone levels above 2 ng/ml, and this in turn can affect the ability of pituitary glands to release adequate levels of Gonadal Releasing hormone (a reproductive hormone), that inhibits cycling. Such cysts can be diagnosed by demonstrating persistently elevated progesterone levels.
h. Ovarian aplasia: It is the failure of ovary to form properly due to a rare congenital problem.
i. Immune-mediated oophoritis: A condition that the body's immune system self destroys the ovary.
This is a failure of the bitch to cycle within 10 to 18 months of the previous cycle. It may be due to low blood thyroid levels, Cushing's disease, ovarian cysts that secrete progesterone, or cortisone administration.