Characteristics of estrus observed by B-ultrasound machine in dairy cows: After the cows reach sexual maturity, they begin to have a series of sexual activity phenomena periodically, such as congestion and edema of the reproductive tract mucosa, discharge of mucus, mental excitement, sexual desire, acceptance of other cows’ mounting, ovarian follicle development and discharge of eggs, etc. The internal and external physiological activities are called estrus, and the stage in which the estrus symptoms are concentrated is called estrus period, and the period from the beginning of one estrus period to the beginning of the next estrus period is called an estrus cycle.

Duration of estrus observed by B-ultrasound machine in dairy cows: The duration of estrus refers to the time from the cow accepting mounting to avoiding mounting. The duration of estrus in cows is short, generally 18 hours on average, ranging from 6 to 36 hours, and some cows can reach 48 hours. Because the duration of estrus in cows is short, and now artificial insemination is being carried out, it is necessary to pay attention to the estrus of cows, so as not to miss the estrus period and lose the opportunity for breeding. Most cows ovulate at night. It is necessary to master its characteristics, grasp the time of timely insemination, and improve the success rate of one insemination.

Observation of cows by B-ultrasound machine: The average estrus cycle of cows is 21 days. The estrus period is affected by factors such as light, temperature, feeding management, and individual conditions. There is a fluctuation range of 17 to 25 days. The estrus period is pre-estrus, estrus, metestrus, and anestrus.

① Proestrus: Proestrus is the preparation period for estrus. The vaginal secretions gradually change from dry and sticky to thin, the secretions increase, and the reproductive organs begin to become congested, but they do not accept other cows to mount them. This period lasts for 4 to 7 days.

② Estrus: The estrus period is the period of strong sexual desire of cows. They show decreased appetite, excitement, frequent mooing, raised tail roots, and are willing to accept other cows to mount them. The vulva is red and swollen, and a large amount of sticky transparent fluid flows out of the vulva. The vaginal mucosa is flushed and shiny, and the mucus secretion increases. In the herd, some cows often sniff the vulva of estrus cows.

③ Metestrus: Metestrus is the period when the estrus phenomenon gradually disappears. The cow's sexual desire disappears and she refuses to be mounted. Vaginal secretions decrease, and the congestion and swelling of the vaginal mucosa gradually subsides. The duration of late estrus is 5 to 7 days.

④ Anestrus: Anestrus is also called interestrus. During this period, the corpus luteum gradually disappears and the follicles gradually develop to the next sexual cycle. The duration of the anestrus period of the cow is 6 to 14 days. After mating, the cow becomes pregnant. This period is called the pregnancy period. The corpus luteum of the cycle turns into the corpus luteum of pregnancy, and no estrus occurs until calving.