The external estrus symptoms of cows correspond to the changes in the internal follicles. The changes in the follicles have been checked by B-ultrasound for cows:

The first period: the cow follicles are hard, and the elasticity is obviously different from the ovarian substance. Very small follicles can be seen on B-ultrasound for cows. The second period: the follicles are slightly fluctuating, the texture is like cherries, the skin is thick, and the volume of the follicles can be seen on B-ultrasound for cows. The third period: the follicles are soft, fluctuating strongly, the texture is like soft-skinned eggs, the wall is thin, and the follicles have a cavity phase (liquid). On B-ultrasound for cows, it can be seen that the follicles can reach 1-2cm. It is not yet time for artificial insemination. The fourth period: the follicles are not fluctuating, tense, and the surface feels hard and full at first. Insemination can be performed when using conventional semen. The fifth period: the follicles are relaxed or there are ovulation pits in the ovarian follicles, and there are follicle skin and liquid for a short time. Failure to ovulate beyond the fifth period may be a symptom of delayed ovulation or follicle luteinization and atresia and other hormone disorders. B-ultrasound for cows can be used for regular observation.

Other judgment criteria in the rectal examination method: Gun method, after the insemination of estrus cows, it is necessary to check whether the semen has reflux phenomenon, and if there is reflux, remedial measures must be taken. But more importantly, it is to see whether there is turbid white purulent mucus attached to the tip of the insemination gun. If the cow is not pregnant this time, it should be used as a basis for determining endometritis during the next estrus. It is best to use cattle B-ultrasound to check this disease.

Observation method, most cows have transparent mucus flowing out during estrus, more or less attached to the middle and upper part of the tail. Due to the low temperature in winter in northern my country, the mucus is frozen into a white and turbid state, so it is important to distinguish. When examining the uterus, pay attention to the discharge of mucus, such as transparent filaments, transparent pus knots, translucent, yellow, or secretions between urine and mucus. Differentiate different symptoms and give treatments respectively. You can also use cattle B-ultrasound to check whether the uterus is accumulating fluid or pus.