Shortened Interestrus Interval in Bitches

Shortened interestrus interval in bitches refers to a condition where the time between consecutive estrus cycles (the period from one heat to the next) is abnormally short, typically less than the normal range of 5 to 11 months.

This condition can occur due to various factors, including incomplete uterine repair after the previous cycle, ovarian abnormalities such as follicular cysts, uterine diseases, or hormonal imbalances. While some breeds naturally have shorter cycles, frequent cycles before the age of 2.5 to 3 years may not require treatment.

Shortened interestrus interval in bitches, caused by various reasons, includes:

1. Idiopathic Shortened Ovarian Cycles
2. Follicular Cysts
3. Uterine Diseases
4. Split Heats
5. Ovulation Failure

1. Idiopathic Shortened Ovarian Cycles

Bitches normally have an interestrus interval of 5 to 11 months. The German Shepherd dog and the Rottweiler are breeds that often have fertile cycles every 4.5 months.

Apparent infertility occurs when a bitch enters proestrus prior to completion of the uterine repair. Infertility could be the result of implantation failure caused by an abnormal endometrium that has not recovered from the previous effects of progesterone.

Prior to making a diagnosis or instituting therapy, a complete history of the bitch must be obtained and studied. The bitch that cycles at less than 4 month intervals is typically normal in all respects and is infertile only as a result of incomplete uterine involution.

Young bitches often have irregular, frequent, or silent ovarian cycles. By the age of 2 to 3 years, ovarian cycles should be regular. Thus, it is recommended not to treat any bitch for frequent cycles until she is at least 2.5 to 3 years of age.

Treatment for the bitch older than 3 years of age that cycles too frequently is to medically induce a normal anestrus period. This can usually be accomplished by treating the bitch with mibolerone drops for a period of 6 months. Medication is started 6 to 8 weeks after the end of the previous standing heat.

One must ascertain that the bitch is not pregnant prior to beginning mibolerone therapy because this potent synthetic androgen causes urogenital defects in female fetuses and the bitch also may undergo some virilization, but these signs are reversible and the drug is not thought to alter future reproductive performance.

The bitch should be bred during the first estrus that follows therapy. This estrus can begin immediately or as long as 6 to 9 months after discontinuation of therapy.

2. Follicular Cysts

Ovarian follicular cysts have been implicated as a cause for shortened interestrus intervals in the bitch. Follicular cysts are well recognized in association with prolongation of proestrus and/or estrus.

Abdominal ultrasonography is the only practical means of diagnosing an ovarian cyst. Treatment includes surgical removal of the cyst or the cyst and ovary.

3. Uterine Diseases

Uterine disease has been suggested as a cause for shortened inter estrous intervals and a diagnosis of this condition requires histologic evaluation of uterine tissue obtained by uterine biopsy.

4. Split Heats

Split heats are observed in young pubertal bitches but can occur at any time in life. In split heat, follicles develop, produce estrogen and the bitch exhibits all signs of proestrus.

However, ovulations do not occur. Four to 10 weeks later, the bitch once again enters into estrus. The second half of split heat is always an ovulatory heat. Diagnosis is by vaginal cytology and serum progesterone estimations.

5. Ovulation Failure

Failure to ovulate may result in failure to form corpora lutea and failure to synthesize progesterone.

The entire diestrus phase of the ovarian cycle is skipped, and, therefore, the phase of uterine involution is also brief. Diagnosis is based on serial serum progesterone determinations.

It is not known how this diagnosis differs from that of split heats. In the bitch less than 3 years of age, no treatment is recommended.

In the bitch older than 3 years of age, an attempt to stimulate ovulation can be undertaken with luteinizing hormone or human chorionic gonadotropin administered the day before or the day after first breeding.