The progesterone levels in dogs can vary depending on different stages and conditions.

Based on the information provided in the reference article, here is a summary and breakdown of the appropriate ranges of progesterone levels in dogs:

Progesterone Levels during Estrus:
During estrus, the concentration of progesterone varies throughout the estrus cycle.
The average progesterone concentrations at LH-1 and LH0 are 1.7±0.7 ng/ml and 2.7±0.6 ng/ml, respectively.
Ovulation occurs approximately 48-60 hours after detecting LH0, during which time the progesterone concentration rises, with average serum progesterone concentrations of 4.8±0.9 ng/ml and 7.2±1.3 ng/ml at LH+2 and LH+3, respectively.
During the fertile period (LH+4 to LH+7), the progesterone concentration ranges roughly between 10ng/ml and 20ng/ml.

Determining the Optimal Breeding Period based on Progesterone Levels:
By tracking changes in progesterone levels, the optimal breeding window can be identified. The rise in progesterone levels begins after the LH peak.
The optimal breeding period typically falls between the 4th and 7th day after the LH peak.

Other Applications of Progesterone Levels:
Monitoring progesterone concentrations can also be used to predict the delivery date, as a progesterone concentration of less than 1ng/ml indicates a 100% chance of cervical dilation within 24 hours.
Progesterone testing can also help determine if "fetal protection" is needed, i.e., whether exogenous progesterone supplementation is required during pregnancy.
It can assist in detecting reproductive system diseases, such as emotional agitation, delayed development, and decreased libido.
It can be used to determine the sterilization status of female dogs.

Please note that the above values are average and ranges based on general research and statistics. Actual conditions may vary due to individual differences, age, weight, breed, and other factors. Therefore, in practice, progesterone testing and analysis should be conducted according to the veterinarian's recommendations and specific circumstances.