Progesterone

Progesterone is a sex hormone that maintains pregnancy in female dogs and regulates the reproductive cycle.

After ovulation, the corpus luteum in the ovaries produces this hormone. It transforms the uterine lining and prevents premature labour. Without sufficient progesterone, a pregnancy cannot be maintained, as the body would expel the foetuses.

Progesterone affects not only the uterus but also behaviour. Therefore, female dogs in heat often become more clingy or start nesting with toys after ovulation.

How does progesterone affect the oestrus cycle?

The progesterone level determines which phase the female dog is in.

During pro-oestrus (first bleeding), progesterone is low, and oestrogen dominates. The vulva swells, and bleeding begins. Approximately 9 to 12 days later, ovulation occurs. Now progesterone rises sharply and remains elevated for 2 to 3 months, regardless of whether the female dog is pregnant or not.

This explains why unspayed female dogs go through a hormonal change after every heat. The body behaves as if it were pregnant for months. Only when progesterone drops does the resting phase (anoestrus) begin until the next heat.

When is a progesterone test useful in dogs?

A progesterone test helps with determining the mating time and monitoring pregnancy.

Breeders use it to determine the optimal mating time. Ovulation occurs approximately 24 to 48 hours after the progesterone rise above 2 ng/ml. Since sperm can survive for up to 7 days, the time window is wider than often assumed.

In cases of pregnancy problems, the vet regularly measures the progesterone level. If it drops below 1 ng/ml from day 58 onwards, birth is imminent. A drop that is too early can indicate premature births.

The test also brings clarity in cases of cycle disorders: if progesterone remains permanently low, ovulation probably does not occur. Unusually high values may indicate ovarian cysts.

What happens in a false pregnancy?

A false pregnancy arises from the normal hormone drop after heat.

Approximately 6 to 12 weeks after ovulation, progesterone drops abruptly. At the same time, prolactin, the milk-producing hormone, rises. The female dog shows all signs of a real pregnancy: nest building, protecting toys, and even milk production.

This is a normal physiological process and generally harmless. Most female dogs go through at least one noticeable false pregnancy. A vet visit is only required in cases of extreme behavioural changes or excessive milk production.

Can progesterone deficiency be treated?

In cases of proven deficiency, the vet can supplement progesterone, but only under strict control.

Values that are too low during pregnancy can lead to premature or stillbirths. Progesterone preparations, which are usually administered as an injection or gel, help here. The dosage is based on blood values and must be adjusted continuously.

Too much progesterone can promote uterine inflammation (pyometra). This life-threatening disease occurs particularly in older, unspayed female dogs. Therefore, hormone therapy should always be left to the vet.

Supplementation usually stops a few days before the calculated due date, as otherwise progesterone can block natural labour contractions.