When using cattle B-ultrasound for early pregnancy testing, the accuracy of the test varies at different time stages. The accuracy of diagnosing empty pregnancy in multiparous cows on the 20th day of pregnancy is low, at about 60%. The reason is that the diameter of the embryonic sac of early pregnant cows is generally less than 1cm, and the resolution of medium-performance cattle B-ultrasound is not enough. During the inspection, due to various foreign body interferences, accurate and clear images cannot be obtained, and thus accurate judgments cannot be made.

The accuracy of diagnosing pregnancy in the three time periods of 20-28 days is higher, because cattle B-ultrasound examination can confirm the diagnosis as long as a clear embryonic sac image is seen, which is generally accurate. However, due to differences in individual dairy cows and the performance of cattle B-ultrasound, it is not possible to accurately determine empty pregnancy if a clear embryonic sac image is not seen.

When using cattle B-ultrasound to check for early pregnancy in young cows, the diagnostic accuracy of young cows at 20-28 days is significantly higher than that of multiparous cows, especially the diagnostic accuracy of young cows is as high as 100%, indicating that the early pregnancy diagnosis effect of cattle B-ultrasound in young cows is better than that of multiparous cows. The reason may be that multiparous cows generally have a deeper uterus, slight sagging, thicker uterine wall, and more fat accumulated nearby, while young cows have a shallower uterus, no sagging, and no fat accumulation near the uterus.

When using cattle B-ultrasound for diagnosis, the ultrasound image of young cows is clearer than that of multiparous cows, and the confidence of diagnosis is higher. Therefore, the time of pregnancy diagnosis after mating of young cows can be appropriately advanced. The diagnostic accuracy of young cows and multiparous cows is 100% at 29-40 days. During this period, both achieve ideal results in cattle B-ultrasound diagnosis.