Infertility

19 Infertility

There are many reasons for infertility in female dogs (Figure 19-1). The diagnostic scheme used varies with cycling activity of the bitch.

Figure 19-1 Algorithm for female infertility.

If the bitch has not cycled by 24 months of age, that is primary anestrus. Possible causes of primary anestrus include the following:

• Previous ovariohysterectomy (OHE). Bitches spayed when very young may have a tattoo in the groin. A scar may be palpable on the abdominal midline; abdominal surgery for OHE cannot be differentiated from abdominal surgery for another reason by physical examination alone. Measurement of luteinizing hormone (LH) or estrogen may be used to determine whether a bitch has been spayed.

• Silent heat. Bitches may go through the ovarian changes of heat, with development of follicles that ovulate normally, but exhibit none of the external signs of heat, such as vulvar swelling and bloody vulvar discharge. To determine whether bitches are cycling silently, serial vaginal swabs and measurement of progesterone in blood must be performed.

• Overwork or malnutrition. Bitches worked excessively or on a poor plane of nutrition may fail to cycle. Body condition can be assessed in dogs by evaluation of the dog’s silhouette from above and palpation for the ribs and spines of the vertebrae (Figure 19-2). Dogs that are excessively thin (Figure 19-3) or excessively heavy (Figure 19-4) will not cycle normally. Decreasing the working or show schedule, ensuring adequate nutrition and body condition, and housing the bitch with cycling bitches may induce her to cycle.

• Hypothyroidism. Hypothyroidism is discussed in detail in Chapter 6. The most accurate diagnostic scheme for identification of hypothyroidism in bitches is measurement of free T₄ by the dialysis method and determination of TSH concentrations. Thyroid hormone values are not affected by working and training of dogs. If the animal is ill, concentration of T₄ may be artificially decreased, but the concentration of TSH should be unaffected.

• Systemic disease. Animals that are unhealthy are less likely to cycle. Complete blood count, serum chemistry profile, and urinalysis should be performed to assess general condition of the dog.

• Chromosomal abnormalities or abnormalities of sexual development. Identification of chromosome number and type in the bitch (karyotype) may allow identification of this cause of primary anestrus. Some dogs have a normal chromosome complement but have abnormal gonadal development; this usually is diagnosed by histopathology after surgical removal of the gonads.