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Reproduction in pigs

One of the big advantages of farming pigs is their ability to reproduce.

Sows can produce over two litters per year with in excess of 20 piglets weaned. This is a very high reproductive rate compared to cattle and sheep for example. This article covers the basic information you need to adequately manage breeding pigs.

When to breed

As many as 85-95% of sows return to oestrus (i.e. will stand for the boar) within four to seven days after weaning, so plan weaning around the availability of a boar and have him present before you wean.

How to detect pigs in heat

At weaning, place the sow in a pen next to the boar so that she is aware of his presence. On day three after weaning the sow should be checked twice daily for signs of heat. The initial signs are reddening and swelling of the vulva but the sow is only ready to accept the boar when she stands still to pressure applied to the back by pressing firmly on the rump and lower back. If the sow stands still without attempting to get away she is ready for the boar.

How to manage the boar

If you only have a small number of sows it is not necessary to prevent overuse of the boar so the sow can be run with the boar and nature be allowed to take its course.

For supervised matings, allow two matings 24 hours apart if you are confident at heat detection. If not then three matings 12 hours apart is recommended.

Put the sow with the boar and wait while they mate. A successful mating is usually completed in three to five minutes. The boar will spend some initial time nudging the sow before mounting and if the sow attempts to avoid contact with the boar at this stage she is not ready.

After mounting make sure that he has entered the sow. It is recommended to gently direct the pizzle by holding the sheath if the boar is having difficulty. Boars quickly get used to this manipulation. A gelatinous clump is often discharged onto the ground after a mating, this is normal and does not mean that the mating was unsuccessful – in fact it is a good sign.

After a successful mating, separate the pigs and repeat the process in 12 to 24 hours. Boars are capable of servicing 2-3 sows per week (each service comprising 2-3 matings) for an indefinite period if the matings are supervised. His fertility is likely to be lowered if he is overworked or if not used at least once a week, so keep him occupied.

Reproductive values you need to know

 1st heat after weaning  4-7days
 Time between heats 21 days (± 3days)
 Gestation (pregnancy) length 114 days (3 months, 3 weeks, 3 days)
 Puberty 180-190 days of age


Factors affecting sow performance

Management has a major influence on sow performance. By following some basic principles, sow performance can be maintained at a consistently high level.

Sow Factors:

  • Farrow sows in body condition score (BCS) 4. The scale is 1-5 with 5 being over-fat.
  • Overweight sows (BCS 5) are prone to:
    • Farrowing difficulties
    • Overlaying/crushing piglets
    • Reduced litter size at next mating
    • MMA (see later)
  • Underweight sows (BCS 3 or less) are prone to:
    • Increased weaning to first service interval
    • Reduced litter size at the next mating
  • On average, sows perform best from the 3rd through to the 5th litter. After the 5th litter the number of pigs weaned per litter begins to decrease. Increased numbers of stillborns, smaller litters, farrowing difficulties and overlaying/crushing are the contributing factors. Some sows continue to perform well but the trend is downward, so don’t hold onto sows for too long.


  • Infectious disease is a significant contributor to the SMEDI syndrome – stillborns, mummies, embryonic death (long returns) and infertility. Acceptable targets are:
  Target %
Piglets stillborn  <5%
Piglets as mummies <0.5%
Abortion rate <0.8%
Farrowing rate* >85%

*Farrowing rate is the number of sows/gilts farrowing as a percentage of the number mated

  • Parvovirus and Leptospirosis are the two most common infectious causes of poor fertility. Because they are so widespread, vaccination against these diseases is strongly recommended. Sows require boosters 6 monthly and gilts should be vaccinated before mating.


MMA: Mastitis Metritis and Agalactia

This has a devastating effect on some litters. The affected sow fails to let down her milk and by the time she recovers two to three days later the entire litter may be lost. Treatment often gives disappointing results because it is started too late, so early detection and intervention is important.

A more effective option is to have a prevention strategy in place. The disease is not fully understood but E. coli and other bacteria that are commonly found in faeces are the most likely cause, so hygiene is important along with these other strategies.

  • Avoid sows becoming overweight
  • Do not overfeed sows in the three days before farrowing (1kg/day is sufficient)
  • Increase feed intake gradually after farrowing
  • Maintain good hygiene (clean solid floor pens daily)
  • Scrub sows prior to entry into farrowing pens/crates
  • Remove from group pens up to seven days before farrowing (avoids udder injuries)
  • Keep farrowing house temperature inside 18 – 20ºC
  • Once the sow has finished farrowing, provide 10 litres of fresh water in the feeder (nipple drinkers can have insufficient flow for sows to rehydrate adequately after farrowing)
  • During periods of higher MMA incidence, in-feed antibiotics may be necessary until management changes catch up with the problem (e.g. avoiding overweight sows)

This is just an overview of a complex area. Problem-solving requires discussion at an individual level, so we encourage you to contact us with any enquiries you may have.