Proper use of ultrasound for pregnancy testing

Each examination takes about 30 seconds. Pregnant sows can be tested starting 24 days after mating; results from testing within 21 days after mating may be unreliable, so two pregnancy tests should be performed on site for confirmation.

The best scanners can achieve 99% accuracy in detecting non-pregnant sows, identifying almost all empty sows. All scanners can display normal embryonic vesicles, but only good scanners can clearly show an image of a uterus without embryos on the screen, so as to confirm that the sow is not pregnant.

On site, pregnant sows are rarely misdiagnosed as non-pregnant. However, some non-pregnant sows may be misdiagnosed as pregnant. Common sources of misdiagnosis include mistaking dark spots for embryonic vesicles and thus concluding the sow is pregnant, or mistaking multiple small dark spots formed by fluid in the uterus for early pregnancy or suspected pregnancy.

II. Impact of ultrasound scanning on non-productive days.

Scanning results from two herds showed that non-pregnant sows detected at the first scan accounted for an average of 34 and 42 non-productive days.

Most sows detected as pregnant but subsequently returning to estrus can be identified within a very short time after scanning.

Sows detected as pregnant but subsequently returning to estrus within a short period indicate that the sow was in fact non-pregnant at the time of testing.

This raises a question: how should we conduct pregnancy testing on site?

III. How should we scan sows?

Remember, we always start testing with sows that have not returned to estrus or shown signs of estrus at 24 days of gestation and 21 days after mating.

1. Make sure these pigs are always easy to approach after entering the barn, and test them in a quiet manner to prevent stress or disturbing them.

2. At the same time, keep the sow in a standing position

3. Apply gel to the scanner probe and place it at the inguinal area.

4. Make sure arms, hands, knees and toes do not press on the device.

5. Slowly move the probe until a clear fetal image is found.

6. If the image appears blurry, apply more gel.

7. Pregnancy can only be confirmed when at least two clear embryonic vesicles are found.

8. If no embryonic vesicles can be found, scan the other side.

9. If uncertain about the diagnosis, mark the sow and re-scan one week later.

10. Mark non-pregnant sows and then move them to the breeding barn.

If the farrowing rate on some farms is below 85%, it is recommended to check again at the 6th week of gestation. Early detection of infertile sows is the key to shortening non-productive days and thereby maximizing reproductive efficiency.

The most effective way to manage non-productive days is to identify returning sows during the first normal return-to-estrus interval of 18 to 25 days after mating. The breeding team should, through routine estrus checks, correctly identify more than 60% of gilts and sows that have not conceived within 18 to 25 days after mating, and should also be able to use real-time ultrasound examination to confirm more than 90% of non-pregnant sows.

Note,after mating, a sow may return to estrus at any time between 25 and 30 days as a non-pregnant state, but most sows will return to estrus within 18 to 25 days.

IV. Pregnancy testing work should be carried out differently at different time periods:

• From after mating until the sow is moved onto the farrowing crate. Persisting with at least one boar estrus check every day helps stockpeople find sows returning to estrus and sows that have not conceived.

• 18-48 days after mating. "Pregnant" sows will not show estrus symptoms in the presence of an adult boar. This will detect regular and irregular returns to estrus.

• Around 28 days of gestation. Real-time ultrasound imaging is very effective in checking pregnancy status (99% accuracy). For sows that are in question and uncertain, they can be checked again 35 days after mating (see Figures 2.8-2.13).

• 8 weeks of gestation. At this time, pregnancy or non-pregnancy can be observed with the naked eye from changes in the sow's abdomen, and this can serve as the final pregnancy check (see Figures 2.14-2.15).

Ultrasound image of a non-pregnant sow

17 days of gestation, embryonic vesicles (uterine vesicles) are difficult to identify

28 days of gestation, embryonic vesicles are easy to identify, note the embryonic image

35 days of gestation, note the easily visible embryonic image and obvious embryonic vesicles

Beyond 80 days of gestation. Fetal bones become more obvious, but the fetal pig image is difficult to see against the maternal background. Note: the sow's intestines look like uterine vesicles, but without a clear boundary. Because allantoic fluid is significantly reduced, it is difficult to see the fetal pig against the background of the sow's abdomen.

Around 35 days after mating. Note that although there appear to be "black hole"-like embryonic vesicles, there is no embryo. Sometimes a "grain"-like filling can be seen in the uterine cavity.

For identification difficulties see Figures 2.13-2.15.

Around 8 weeks of gestation: differences between non-pregnant and pregnant sows can be seen by visual observation. The ventral side droops and bulges.