Seasonal Infertility

What is it?
A drop in fertility performance in gilts and sows in the summer and early autumn. It usually manifests in two ways:

1. More difficulty coming on heat

  • Delayed puberty in gilts
  • Increased time between weaning and coming on heat
  • Higher anoestrus rate

2. Increased early pregnancy failure rate, usually detected as irregular returns to service 25 – 35 days after breeding.

Overall farrowing rate can drop 10-15%. To assist in combating this problem, ensure accurate heat detection and pregnancy diagnosis.
The syndrome has been studied globally for over 40 years, but is still poorly understood. It is very unpredictable; it can vary hugely on farm year to year, and even shed to shed on the same farm.

What causes it?
We don’t know! It must be related to the long daylight hours of the summer and early autumn and / or the higher environmental temperatures at that time of year. It is seen from Scotland – long day length, but not particularly high temperatures, to Australia.
There are a number of key risk factors identified by research:

Sows which:

  • Are parity 6 or higher
  • Take longer than 5 days to return to oestrus after weaning
  • Are early weaned
  • Wean fewer than 8 piglets

are at a greater risk

These factors also contribute to poor fertility throughout the year, suggesting that seasonal infertility may be more likely seen in sows of questionable fertility, or those subjected to poor management.
More recent research indicates that the symptoms may be caused by earlier ovulation during the summer and / or reduced hormonal support of the pregnancy 3 to 4 weeks after breeding. The eggs which ovulate may also be of poorer quality.

Minimising the Effects
Although we do not understand the disease fully, we can mitigate the risk factors illustrated above, pertaining to increased farrowing rate.

1. Maximising nutrient intake by lactating and weaned sows.

2. Providing cooling for lactating and weaned sows.

3. Providing additional boar stimulation for oestrus after weaning, e.g. use vasectomised boars!

4. Group housing sows between weaning and mating/insemination.

5. When grouping gilts or sows, ensuring you match them closely for size/weight.

6. Ensuring gilts and weaned sows are not overcrowded.

7. Mating/inseminating during the cooler parts of the day.

8. Increasing the frequency of heat checking to twice daily in the seasonal infertility period, and mating/inseminating sows at first heat detection regardless of when they return after weaning, given the recent finding that sows appear to ovulate earlier in the heat period during the summer/autumn period. Once the first mating/insemination has occurred, further matings/inseminations can be provided at 24-hour intervals, as normal.

9. Housing mated/inseminated gilts and sows individually, or maintaining them in stable groups from before mating/insemination until at least four to five weeks post mating/insemination. (Mixing gilts in early pregnancy is risky, especially if it occurs after day four post-mating/insemination).

10. Individually feeding mated gilts and sows, at least for the first four to five weeks of gestation.

11. Conducting more frequent and rigorous checks for gilts/sows returning to oestrus between days 18 and 32 post-mating/inseminating.

12. Applying a good pregnancy diagnosis procedure at four weeks post mating/insemination, and again three to four weeks later.