Pork production: Repeating sows and your boars


By Digital team | 11 June 2018
pig farm; biosecurity; pork; sows
A boar and his sows in an unconfined system with sound fences. A good fence goes a long way to biologically securing a farm.

Question: I have a serious problem – nearly 50% of my sows repeat (come on heat after being served). I use 3 boars but, while the problem occurs in sows served by all the boars, it occurs more often with 1 of the boars. Can this be caused by a disease?

Returns to service can be caused by a disease, but there can also be other reasons.

The main ones are:

  • That the sow is served too early or too late in her heat cycle and the ova (eggs) are not where they should be for the sperm to reach them.
  • That the sows have an infection in the reproductive tract (which may have come from the boar), which causes unfavourable conditions for the embryos to develop.
  • That the boar is not fertile or is not serving successfully; for example, if he is too old.
  • That the boar has an infection of the testicles that causes the sperm to be infertile.

To have the best chance of successful service, the sow should be in standing heat. You can test for this by pressing firmly on her back with both hands. If she stands firm without trying to move away, she is in standing heat.

Once she’s in standing heat, she should be served twice in the next 24 hours (8 to 12 hours after standing heat is detected and again 12 hours later). If she is still in standing heat, another service 12 hours after that should ensure fertilisation.

Also read: Do pigs become infertile in summer?

In commercial herds, boars usually only serve for 2 years, starting at the age of 10 months to a year, and being culled when they are 3 years old. Most boars can serve successfully for a year or 2 more, but it’s always important to observe the boar when serving to make sure that he is penetrating the sow – he should remain mounted and active for a few minutes and not fall off straight away. If the size of litters gets smaller or you can see there’s a problem related to a boar, it would be better to replace him.

Observe the sows to see if there is any discharge from the vagina or whether they show signs of straining when urinating. These can be signs of an infection of the lower reproductive or urinary tract that might prevent conception. You will need veterinary help to solve this problem.

Also read: When are sows in heat and how long are they pregnant?

Examine the boars for any signs of genital infection, such as pus discharging from the penis. The testicles should be normal size (and the same size), they should feel firm but not hard, and they should feel cooler than the rest of the body.

If they feel warm, hard or lumpy inside, there’s probably an infection and you’ll need veterinary help. You could decide to cull the boar as the testicles may be permanently damaged if the infection has been ongoing for a long time.

  • This article was written by Dr. Mary-Louise Penrith and first appeared in Farming SA.