Dog Breeding Cycles and Seasons

It never fails: when your dream litter is planned, your bitch never comes in season. And when you have no intention of breeding, it seems she will never go out of season. Some natural variation in timing is normal, but when is too longor too shortreally too wrong?

Once she's had one estrous cycle, your bitch should normally come into season again five to eight months later. Some breedssuch as German Shepherd Dogs, Rottweilers, Basset Hounds, Cocker Spaniels, and Labrador Retrievershave a naturally shorter interval between seasons, while others, most notably Basenjis, have a longer interval. Some bitches have silent heats, in which they ovulate but have no behavioral or physical signs of being in estrus. Unless a wily stud is around, you may not realize she's in season without the aid of monthly serum progesterone tests, or weekly vaginal smears to check hormonal or cellular changes consistent with estrus.

For most non-Basenjis, if she hasn't cycled 10 to 18 months after her previous season, she is said to have secondary anestrus. Hypothyroidism, hyperadrenocorticism, luteal cysts, and glucocorticosteroid treatment may all cause secondary anestrus, so treatment depends on the cause. If no underlying cause can be found, several drug protocols for estrus induction are available. However, even if they bring on estrus, matings often do not result in pregnancies, and some undesirable side effects are possible.

Sometimes the time between seasons is too short. Uterine disease, such as cystic endometrial hyperplasia, can cause premature return to estrus. If the anestrus period is shorter than four months, matings are usually unsuccessful. This may be because the canine uterus requires 130 to 150 days for endometrial involution and repair following estrus; without sufficient time, the uterus may not be ready to sustain a pregnancy. Treatment with mibol-erone, an androgen drug that maintains anestrus, can prolong the period between seasons sufficiently for the uterus to prepare for a successful pregnancy. Failure to ovulate during a preceding season has also been linked to a shortened anestrus. In this case, the subsequent season is often normal and fertile.

Don't confuse a short cycle with a split season, in which a bitch either goes out of season after proestrus, or has a very short estrus but then comes back into season after only a few weeks. Matings that occurred during the first apparent estrus are usually unsuccessful, but matings in the second estrus are often successful. An occasional split season is usually not cause for concern, but repeated incidents may indicate a hormonal problem.

When do 21 days feel like 21 weeks? When your bitch is in season, you don't intend to breed her, and your males are going crazy. Even if you don't plan on a breeding, it's important to record dates so you know if she's really been in too long. Persistent estrus is defined as a combined proestrus and estrus lasting longer than six weeks. It's critic al to know whether it's the proestrus or the estrus phase that is running too long.

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