What causes seasonal infertility in pigs and how to manage it

Infertility often spikes during late summer and early autumn. Dr Grant Walling, director of science and technology at breeding company JSR, offers some ways to manage breeding problems this summer.

Infertility is a costly problem in pig herds, with every additional day a sow is empty costing up to £2.70.

The target should be to get sows in pig with two inseminations over a 24-hour period, assuming the sow demonstrates standing oestrus for the second serve.

For a small number of sows (<20%), a third service may be required if they continue to demonstrate standing oestrus.

Why can fertility drop in the summer/early autumn?

Infertility can affect many pig herds in late summer/early autumn as a result of declining daylight hours and increased temperature (see table, below).

Reduced conception rates are often seen for animals served in August and into September, although the specific week varies from farm to farm. 

It is also dependent on facilities, with outdoor herds more adversely affected than indoor herds with a controlled environment.

See also: Single-parity move lifts pig herd performance

The main impact on sow production is reduced farrowing rates. Average farrowing rates should be in excess of 85% with a target in excess of 90%. However, during the late summer it is not uncommon to see rates drop to as low as 65% on badly-affected farms.

For those using natural service, extremes of temperature can also affect boar semen production and the boar’s libido.

A study by AHDB Pork found gilts to be less affected by seasonal infertility because they do not have the added heat generation from lactation – heat production naturally increases as lactation progresses. This is because the sow produces more milk.

This extra heat production, combined with increasing and extended exposure to environmental temperatures, can leave sows susceptible to heat stress, especially just before weaning.

Heat-stressed sows will not eat as much. This can have a negative impact on the development of follicles on the ovaries. Nutritional deficits are also associated with a lower production of the luteinising hormone (LH), resulting in delayed returns to oestrus and reduced conception and farrowing rates.

What can be done to manage seasonal infertility?

  • Monitor sow feed intake in warm weather.
  • If sows are not eating, take steps to cool them down or provide more energy-dense feed.
  • In outdoor systems, provide wallows early in the year as well as throughout summer, or sprinklers for sows to cool down.
  • Paint farrowing arcs white to reflect sunlight and reduce the temperature inside; painting huts white can reduce internal temperatures by about 7C.
  • Use insulated arcs, fully insulated where possible.
  • Use an adjustable ventilation opening at the rear and re-align arcs to assist with air flow.
  • Feed sows at least twice a day, if not on an ad-lib system.

How can you mitigate the impacts of heat stress?

Having extra stock to replace any sows failing to get in pig can help ensure farms run at capacity.

It is worth considering increasing gilt numbers in May to ensure the system continues to run at target during the later summer months when seasonal infertility causes the most problems.

Gilts bought at 24 weeks old in May will need 10 weeks of acclimatisation to reach their recommended age at first service. For example, a gilt arriving on 24 May won’t be at her recommended service age until 3 August.

Farmers breeding their own replacements should have a system that supplies the required numbers of new gilts in every batch. It is always better to have too many pigs available and apply a more focused selection than to be short.

Typical seasonal infertility pattern for pregnancy losses

  Spring Summer
Number of sows 135 175
Three-week returns 5 14
Negative pregnancy test 5 22
Abortions 1 4
Adjusted farrowing rate 91.9% 77.1%
Source: O’Leary, Final report to Pork CRC, 2010

What other issues can cause infertility?

Changes in genetics

  • Larger litter sizes with a new genotype can put pressure on the sow. If the lactation ration hasn’t been adapted to cope with extra numbers of piglets being weaned, sows can start mobilising excessive levels of body reserves, leading to poor condition at weaning, and interruption to ovulation.
  • Gestation lengths vary and may change with a change in genotype. Therefore, it is important farm staff detect and map oestrus prior to service and do not simply inseminate on a specific day of the week.

Semen storage

  • If semen isn’t stored correctly it can be damaged, rendering it useless, especially during hotter periods. It is important semen is kept at the correct temperature and is turned at regular intervals.
  • Semen should be stored at a constant temperature of 16-18°C. Use a temperature controlled box for storage complete with a maximum/minimum thermometer, which should be checked daily.

Age of the sow

  • Older sows are more prone to seasonal infertility and sows in parity six or above tend to see declining fertility. Therefore, replacing older animals before this may be preferable.

What are the implications of not managing problem sows?

Managing problem sows is important as animals that return to oestrus after a service are statistically far more likely to return to oestrus if they are served again, in comparison with bringing a gilt into the herd.

Assessing data from herds that give animals a “second chance” shows that up to 80% of the returns come from animals which had returned to oestrus previously.

Carrying sows with sub-optimum fertility also reduces pig numbers and could mean more pigs having to be bred to produce the right number of finishers.

Data shows that for each 10% increase in the farrowing rate of bred sows, there is a corresponding increase of 2.63 live pigs born a sow a year.

Problem sows

A problem sow is one that fails to fit the system on the farm. This can include:

  • Animals with elongated weaning-to-service intervals. The target should be six days or less.
  • For producers running two-week or five-week batch systems it is those sows that fail to hold to their first service after weaning, as it is very difficult to get them back into a breeding group.
  • Sows that return to oestrus after a service on weekly systems. They are up to 80% more likely to return to oestrus if they are served again.

Should you hold on to problem pigs until the cull sow price lifts?

No. While the cull sow price currently is reasonably good at £1.18, that sow needs to be replaced, and with the slaughter price at £1.64 (and given that a large proportion of the gilt price is related to slaughter value), any advantage of one is offset by the other.

Farmers should be looking to set their replacement strategy based on the needs of the farm rather than the small weekly variation in the price.