There are various methods to detect pregnancy in dogs, including observing physical and behavioral changes, abdominal palpation, radiological diagnosis, ultrasound diagnosis, and blood tests.

Here's a detailed introduction to these methods:

I. Observing Physical and Behavioral Changes

• Mammary Gland Changes: After conception, a dog's mammary glands will become larger, thicker, and more prominent. In the later stages of pregnancy, the glands will become fuller and swollen, and sometimes liquid may be secreted from the nipples.
• Body Shape Changes: The dog's body shape typically starts to change around the 4th to 5th week of pregnancy, with the waist thickening and the abdomen gradually protruding. By the last three weeks of pregnancy (6th-9th week), the dog's belly will become round and swollen.
• Behavioral Changes: In the last three weeks of pregnancy, the dog's protruding belly may make movement more difficult, causing it to sleep more than usual. Additionally, dogs may become more docile and affectionate, or exhibit unusual behavior due to discomfort or anxiety.
• Appetite Changes: Early in pregnancy, dogs may become more selective or lose their appetite. However, towards the later stages, their appetite may increase due to the increased nutritional demands of the fetuses.

II. Abdominal Palpation

Abdominal palpation is a simple but relatively crude method of detection. About a month after mating, the owner can place their fingers together, press gently against the abdomen over the uterus, and slide along the uterine horns. If they can feel the presence of embryonic vesicles within the uterus, it may indicate pregnancy. However, this method requires experience and skill, and it's best performed under the guidance of a veterinarian.

III. Radiological Diagnosis

Radiological diagnosis, such as X-ray examination, is typically used in the later stages of pregnancy to count the number of fetuses in the uterus. This method can only detect fetuses after their bones have developed, so it's generally performed after 45 days of pregnancy. X-rays can clearly distinguish the fetal skull and skeletal structure, providing important information for delivery and post-natal care.

IV. Ultrasound Diagnosis

Ultrasound diagnosis (B-mode ultrasound) is a relatively accurate and commonly used method to detect pregnancy in dogs. It can provide an accurate diagnosis as early as 20 days after mating. As the fetuses grow, ultrasound can also detect fetal heartbeats and count the number of fetuses. Ultrasound diagnosis is non-invasive, safe, and accurate, making it a preferred method among veterinarians and pet owners.

V. Blood Tests

Blood tests are the most accurate and reliable method to detect pregnancy in dogs. By measuring the presence of a pregnancy hormone called relaxin in the dog's blood, one can confirm pregnancy. Once relaxin is detected, it confirms that the dog is pregnant. This method is applicable at all stages of pregnancy but may be more costly compared to other methods.