Ovarian function best monitered using vaginal cytolgy, serum progesterone concentrations

Q. Please review normal and abnormal ovarian function in the dog and cat.

A. Dr. Shirley D. Johnston at the 28th World Congress of the World Small Animal Veterinary Association in Bangkok, Thailand, gave a lecture on normal and abnormal ovarian function in the dog and cat. Some relevant points in this lecture are provided below.

Factual information

The bitch exhibits estrus every five to eight months. There is no significant seasonal influence in most dog breeds. The puberal estrus occurs between 6 months and 24 months of age, with average onset at 10 to 12 months. Stages of the estrus cycle include proestrus (three to 17 days), characterized by ovarian follicular growth and sanguinous vulvar discharge; estrus (three to 21 days), characterized by ovulation and receptivity to mating; diestrus (about 60 days) characterized by luteal progesterone secretion in the pregnant and non-pregnant female; and anestrus (about 4.5 months) which is a time of reproductive quiescence. The bitch is a spontaneous ovulator, ovulating primary oocytes (on average) 24 to 72 hours after a burst of luteinizing hormone (LH) secretion from the anterior pituitary gland; the burst coincides, on average, with onset of behavioral estrus. Both onset of proestrus and onset of estrus, however, are not precise indicators of ovulation in the bitch. The bitch exhibits preovulatory luteinization, with elevation of serum progesterone to concentrations exceeding 1.0 ng/ml occurring as early as two days before ovulation.

The queen is seasonally polyestrus, cycling every four to 30 (14-19 modal) days in the presence of a day length of, or exceeding, 14 hours. Prolonged anestrus results from decreasing day length, and estrus onset results from increasing day length.

Onset of puberty occurs at 4 to 12 months of age and is influenced both by photoperiod and body condition of the queen. Stages of the estrus cycle include proestrus (one to two days), exhibited in only a few queens; estrus (two to 19 days), which is the follicular phase and time of receptivity to mating; postestrus (two to seven days) which is an interestrous interval in queens that are not bred; diestrus (about 45 days if not pregnant, about 60 days if pregnant) which is the luteal phase that follows induction of ovulation; and anestrus (about three months) which is time of reproductive quiescence in late-autumn months in queens exposed to a natural photoperiod. The queen is an induced ovulator and requires more than one copulation to ensure ovulation.

Principles of ovarian function

Ovarian function is best monitored in the dog and cat using a combination of serial vaginal cytology, a measure of estrogen impact on the vaginal epithelium, and serial serum progesterone concentrations, which are a measure of luteal function. Progesterone assay is widely available, and, in general, serum concentrations exceeding 1.0 ng/ml are considered evidence of luteal function in both species. Serum LH assay is not widely available, except for one ELISA kit available in the United States and Canada; measurement of this hormone is most useful in detecting absence of ovaries due to previous ovariectomy or ovarian dysgenesis when LH concentrations are high.

Abnormal ovarian function

The causes, diagnosis and treatment of abnormal ovarian function in the dog and cat are provided in Table 1.

Table 1: Causes of Abnormal ovarian function in the dog and cat

Primary or persistent anestrus may be caused by prior ovariohysterectomy, an abnormality of sexual differentiation with ovarian dysgenesis (such as 79,XXX in the dog or 37,XO in the cat), immune-mediated orchitis, idiopathic cause that responds to cabergoline therapy (bitch), or inadequate photoperiod to sustain cycling (queen).

Estrus after surgical ovariectomy or the ovarian remnant syndrome occurs in both the queen and bitch. The diagnostic approach with ovarian remnants is to confirm presence of cornified vaginal tissue in the female showing estrous signs (to distinguish those from other behaviors) and to monitor or induce ovulation to achieve serum progesterone concentrations that confirm the diagnosis and luteal structures on the ovarian remnant to facilitate its identification at surgical exploration.

Failure to conceive after normal copulation may occur with ovulation failure, which is detected using serum progesterone concentrations following mating.

Shortened interestrous intervals occur most commonly with premature luteolysis about one month after ovulation in the bitch. If premature luteolysis occurs following fertile breeding, progestational support will need to be provided for pregnancy maintenance (see Table 1). In some species, premature luteolysis has been linked to abnormalities of ovulation, suggesting that ovulation induction at a later estrus may be indicated.

Persistent estrus is confirmed estrus (receptivity to mating with vaginal cornification) for more than 21 days in the bitch or more than 19 days in the queen. Causes of persistent estrus in the bitch and queen include follicular cysts of the ovary or functional granulosa cell tumors, both of which are detectable on ultrasound or surgical exploration of the abdomen. Some, but not all, follicular cysts of the ovary respond to medical attempts at ovulation induction.

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