Negative Diagnosis - MS Schippers Pregtector Doppler Mode D'emploi

C) Negative Diagnosis
In the nature of the way the Doppler PregTector Works, where you are making a positive diagnosis
by recognising a positive signal., negative diagnosis is a little more difficult. If the sow is not
pregnant, the characteristic sounds you have been listening to are absent. You will clearly have to
spend al little longer making a certain as you that what you are listening for is definitely not there,
and that your lack of success is not due just to looking in the wrong place. There are some rules to
follow when confirming a sow open or not-in-pig.
1. Don't make a negative diagnosis on just one test. Before confirming a sow is not pregnant, test
her at least twice, with an interval between tests of as long as can be sensibly arranged, ideally a
week.
2. It Is important to know the service date when making a negative diagnosis. It is obviously quite
easy to confirm a negative if the sow should be ready to farrow, because at that time it should be
very easy to find one or other of the vital sounds of pregnancy, as the uterus presents a large and
easy-to-find target. But the uterus in early pregnancy is small, and can be hidden behind other
organs, which can block the passage of ultrasound, or else place the uterus beyond the range of
the transmitted ultrasound.
3. If the sow is lying down, make her stand up. It can happen that sleeping sows are disturbed
when you begin testing them, and so sometimes you test sows that have just stood up. In early
pregnancy the uterus is small and can displaced behind other organs, for example, the intestine.
When the sow stands up, the various structures in her belly do not immediately fall into their
normal positions, and it can happen that you don't hear the uterine artery because the uterus is
temporarily not in its usual place.
If you test that sow again five minutes later you will quite possibly hear the uterine artery loud and
clear the moment you switch on the PregTector, and so you can confidently mar her as pregnant.
4. To erroneously make a negative diagnosis is not a serious mistake, unless you immediately cull
the sow as a result. Your attention will have been drawn to that sow, and she can be retested at
any time therafter to confirm that she is definitely not in-pig. In the worst case, you would certainly
keep the sow for at least three weeks to check her for return to oestrus and test her again before
culling. If she was pregnant all the time, she will now be three weeks more advanced in gestation,
and the uterus correspondingly larger and therefore more difficult to miss. At least your attention
will have been drawn to that animal as being a potential problem.
On the other hand, a false positive diagnosis, where you confirm a sow pregnant when she is not,
is the most expensive error you can make. There will be a tendency tot ignore that sow, or at least
not pay any special attention to her, and it is not unknown for such sows to be kept for the whole
gestation period, and not be discovered non-pregnant until they fall to farrow. When the cost of
labour, finance, feed and loss of profit on the lost litter is calculated, you will quickly understand
the value of accurate pregnancy detection.
5. Making a negative diagnosis becomes much easier with experience. Once you know that you
can find positive pregnancy, you will be confident that the lack of the sounds can definitely be
taken to mean that the sow is not-pregnant. A practise which does not help negative diagnosis is
just to pregnancy test the doubtful sows. Generally, the mere fact that they are doubtful means that
they will be more difficult. Test all sows systematically, so that you become confident in using the
PregTector on the easy ones as well. Most of them are easy, so the fact that you occasionally come
across one which is not is straight away a possible indication of a problem.
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