The head length and BPD of the small-tailed Han sheep fetus, especially the BPD of the fetus, are the most commonly used indicators in the identification of fetal age. At the same time, there are reports of the use of fetal BPD to identify fetal age in rhesus monkeys, alpacas, dogs, cattle, etc.

Sheep B-ultrasound generally uses a 3.5MHz probe, and the time when the fetal head length and BPD can be measured is generally in the 6th and 7th weeks of pregnancy, respectively. Some people measure earlier, which may be caused by the different frequencies of using sheep B-ultrasound probes. Some people use 5.0MHz sheep B-ultrasound probes. In the early stages of pregnancy, the uterus of the small-tailed Han sheep is still at the front edge of the pelvis and its vicinity. At this time, the use of a 3.5MHz probe can overcome the problem of low penetration of the 5MHz probe, and the state of the entire uterus can be clearly seen in a wider field of view, but because the resolution of the 3.5MHz sheep B-ultrasound probe is too low, the accuracy of the measurement value is not high. From the 9th week of pregnancy, the characteristic BPD image of the fetus appears. At this time, different sections need to be taken to measure BPD and head length, and the accuracy of the measurement value begins to gradually increase.

BXL-V60 for sheep

Due to the characteristics of the 3.5MHz sheep ultrasound probe, the entire monitoring period is longer than that of the 5MHz sheep ultrasound probe. The fetal head length exceeds the detection range of the sheep ultrasound in the 13th week, and the fetal BPD can be measured throughout the pregnancy, so the development pattern of the fetal skull and cranial cavity during the entire pregnancy period is obtained. However, in the late pregnancy (after 100 days), due to the characteristics of multiple pregnancy in small-tailed Han sheep, and the fetal head can be located in any position in the abdominal cavity during this period, it brings considerable difficulty to the measurement, and the average measurement takes more than 20 minutes. Therefore, from the perspective of fetal age identification, the best time to use fetal head length and BPD to identify fetal age should be in the middle of pregnancy (50d-120d).

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