Thursday 3 February 2022

Pig fertility issues

Its fair to say that overall we have had mixed fortunes breeding from our pedigree British Saddleback pigs. One of the two breeding sows we currently have has regularly been 'in pig' whilst the second (her sister) has so far had only one litter plus a couple of false alarms when we thought she might be pregnant but no litter subsequently materialised.  

There are a number of issues in respect of this. Firstly, if there is too long a gap since the previous pregnancy then there is a risk of the sow becoming infertile. Pigs need to have regular pregnancies to remain fertile. The minimum would be one litter per year (which is what we have aspired to up to now) but more reliable in maintaining fertility is two litters per year. Once a litter is weaned at eight weeks of age the sow can be put back with the boar after four or eight weeks. The length of gestation is commonly cited as 3 months, 3 weeks and 3 days. Or 115 days or more or less 4 months, so you can see how the two litters fit in over the course of a year.

The second issue is that sows often do not show obvious signs of pregnancy until quite late. Close observation is needed to see if she stands still for the boar, which is a good sign that she is in heat, or whether she won't stand still which might indicate she is already pregnant, or that there is some problem. Not being kept under constant observation, a further potential sign is muddy hoof prints half down the sow's back.  Another observation to look out for are changes to the sow's vulva which can indicate when the sow is cycling (normally every 21 days). The latter are harder to discern with black pigs like ours. Added to this is that a sow is only fertile for around 2 days each cycle so the window of opportunity for the boar or for using artificial insemination is quite small. 

A third related issue is that nearly four months could go by waiting to see if a sow is pregnant. Once it is confirmed this is not the case further valuable time has been lost and the risk of infertility rises.

One potential way out of these scenarios is to scan the sow. We have recently acquired an ultrasound scanner to see if we can improve our management of pig reproduction. So far I have tried it out with one of the sows. Obtaining the scanned image is one thing, but interpreting the image is another, not having had any training in sonography. As is often the case, reading  text books or scouring the internet for sample images don't readily translate into your own lived experience. Anyhow, after a few attempts I think I have produced an ultrasound image which indicates the sow is in the early stages of pregnancy, although I stand to be corrected and eventually time will tell. I have had a chance to confer with a smallholder friend who scans her prize-winning herd of rare breed pigs which has been helpful. 

The ideal time for scanning a pig is between 24-35 days gestation. Later in the pregnancy the key identifiers of pregnancy in the scanned image will change, for example, skeletal features will become evident. In about 10 days time I will scan the second sow, the one who has as yet had just the one litter, to see if there are any developments with her. By this time it will be 24 days since the boar was showing a distinct interest in her.

The way I read this is the rough sphere marked A
is an amniotic sac with the dark representing 
amniotic fluid. The small feature marked F is a
piglet foetus. The same can be seen less clearly
to the right. 

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