NORMAL OVARIAN FUNCTION IN THE DOG

The bitch exhibits estrus every 5 to 8 months, with no significant seasonal influence in most breeds. The puberal estrus occurs between 6 and 24 months of age, with average onset at 10-12 months. Stages of the estrus cycle include proestrus (3-17 days), characterized by ovarian follicular growth and sanguinous vulvar discharge; estrus (3-21 days), characterized by ovulation and receptivity to mating; diestrus (~60 days) characterized by luteal progesterone secretion in the pregnant and nonpregnant female; and anestrus (~4.5 months) which is a time of reproductive quiescence. The bitch is a spontaneous ovulator, ovulating primary oocytes, on average, 24-72 hours after a burst of luteinizing hormone (LH) secretion from the anterior pituitary, which 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.

NORMAL OVARIAN FUNCTION IN THE CAT

The queen is seasonally polyestrus, cycling every 4-30 (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 (1-2 days), exhibited in only a minority of queens; estrus (2-19 days), which is the follicular phase and time of receptivity to mating; postestrus (2-7 days) which is an interestrous interval in queens that are not bred; diestrus (~45 days if not pregnant, ~60 days if pregnant) which is the luteal phase that follows induction of ovulation; and anestrus (~ 3 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.

GENERAL PRINCIPLES ON CLINICAL APPROACH TO DIAGNOSING ABNORMAL OVARIAN FUNCTION IN THE DOG AND CAT

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 USA 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.

PRESENTING COMPLAINTS OF ABNORMAL OVARIAN FUNCTION

Primary or persistent anestrus. 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), autoimmune orchitis, idiopathic cause that responds to cabergoline therapy (bitch), or inadequate photoperiod to sustain cycling (queen) (Table 1).

Estrus after ovariectomy. Estrus after surgical ovariectomy, or the ovarian remnant syndrome, has been described in both the queen and bitch, though is more common in the queen. 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 so as to achieve serum progesterone concentrations that confirm the diagnosis and that achieve luteal structures on the ovarian remnant to facilitate its identification at surgical exploration.

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

Shortened interestrous intervals. 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 (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. 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 (Table 1).

Table 1. Causes of Abnormal Ovarian Function in the Dog and Cat

REFERENCES

1.  Concannon, P.W., Hodgson B., and Lein D.: Reflex LH release in estrous cats following single and multiple copulations. Biol. Reprod. 23:111-117, 1980.

2.  Diez-Bru, N., Garcia-Real, I., Martinez, E.M., et al: Ultrasonographic appearance of ovarian tumors in 10 dogs. Vet Radiol & Ultrasound 39:226-233, 1998.

3.  Gobello C, Castex, G. and Corrada, Y.: Use of cabergoline to treat primary and secondary anestrus in dogs. J Amer Vet. Med Assoc 220:1653-1654, 2002.

4.  Johnston, S.D.: Premature gonadal failure in domestic dogs and cats. J. Reprod. Fertil. Suppl. 39: 65-72, l989.

5.  Johnston, S.D., Root, M.V., and Olson, P.N.S.: Ovarian and testicular function in the domestic cat: clinical management of spontaneous reproductive disease. Animal Reproduction Science. 42:261-274, 1996.

6.  Johnston, S.D., Root, M.V., and Olson, P.N.: Disorders of the canine ovary. In Canine and Feline Theriogenology, W.B. Saunders Co., Philadelphia, PA, 2001, pp 193-205.

7.  Johnston, S.D., Weber, A.F., Buoen, L.C., and Madl,J.E.: X Trisomy in an Airedale bitch with ovarian dysplasia and primary anestrus. Theriogenology 24: 597-607, 1985.

8.  Lawler, D.F., Johnston, S.D., Hegstad, R.L., Keltner, D.G., and Owens, S.F.: Ovulation without cervical stimulation in domestic cats. J. Reprod. Fertil. Suppl. 47:57-61, 1993.

9.  Lofstedt, R.M, VanLeeuwen, J.A.: Evaluation of a commercially available luteinizing hormone test for its ability to distinguish between ovariectomized and sexually intact bitches. J Amer Vet Med Assoc 220:1331-1335, 2002.

10. Meyers-Wallen, V.N.: Inherited abnormalities of sexual development in dogs and cats. In Recent Advances in Small Animal Reproduction, P.W. Concannon, G. England, J. Verstegen, (ed), International Veterinary Information Service, Ithaca, NY, 2001.

11. Root, M.V., Johnston, S.D., and Olson, P. N.: Estrus length, conception rate, gestation and parturition lengths, litter size, and juvenile mortality in the domestic cat. J. Amer. Anim. Hosp. Assn. 31:429-403, 1996.