Farming Summer Infertility and the Autumn Abortion Syndrome


Now is the time to start planning to avoid this year’s summer infertility problems


The physiological causes of summery infertility and Autumn Abortion Syndrome are not understood.  Obviously it has something to do with the summer season – heat and lighting patterns.   The same event is seen in both hemispheres and particularly affects outdoor pigs where the effect can be particularly devastating in hot sunny summers.

Repro oestrus signs au 1

Pic 1.

Sows returning to oestrus in the autumn months – can you recognize which ones are in heat?


Figure 1.

The farrowing rate by month bred for the Northern Hemisphere (North American Data) and the Southern Hemisphere (Western Australian Data)

However, the issue is not the cause of summer infertility, but how are you going to cope with the summer infertility issues.  While the exact timing may be difficult to predict, the fact that what happened last year and every other year, is just as likely to happen this year!


Figure 2.

The farrowing rate for 3 years from Northern Hemisphere (American data)

The graph clearly demonstrates that the summer infertility occurred at the same time, although the impact to the North American herd varied year on year from only a 3% drop to a 10% drop in average farrowing rate.


Calculating the batch farrowing rate %

The batch farrowing rate % is calculated as:


Formula 1  The batch farrowing rate %


Batch farrowing rate % =



Number of sow which actually farrow in a batch




X 100 %

Number of females actually bred in the same batch

The first essential is to correctly define the batch.  The problem on many farms is “which is the first day of the batch?”   This should be the day after weaning.  Thus for a Thursday weaning, the batch starts on a Friday.  Then all the sows for the batch should be bred over the next 7 days – by the following Thursday.  All these sows will then farrow in a batch – 115 days (112-120 days) later, this will be a Friday (following a Tuesday mating).  Because of the natural spread of the gestation period, sows should enter the farrowing area at least a week before expected peak farrowing date to ensure that all of the sows in a batch farrow in the farrowing area.


Table 1.

Breeding and farrowing events within a batch (webversion interactive)


When is your summer infertility problem going to start?

Records, records  - look at your records.  But the records need to reflect your batching programme not vaguely around some ancient concept of a “month”.  Calculate accurately your batch farrowing rate.  Once the timing of your farm’s summer infertility issue has been established you can plan the farm’s breeding.  


Autumn abortion may be more difficult to predict.  But the same principles can be utilised.  If you acknowledge that more sows will abort in the autumn than normal, ensure that there are more sows pregnant.  There is no excuse not to maintain output per farrowing place.


Table 2.

The batch farrowing rate calculator  -download the excel spreadsheet 


On this farm – in the southern hemisphere – their summer infertility issues started around week 50 (mid Dec) and ended around week 6 (Mid Feb).  This could affect farrowing April to June and if 100kg pigs are finished at 23 weeks of age, this could affect finishing in September to November.


In the northern hemisphere – the farms tend to have summer infertility from breedings mid July to October.  This affects farrowing in November to February and finishing from April to July.


A key component to farming summer infertility and autumn abortion syndrome is accurate pregnancy diagnosis.  Real time ultrasound pregnancy diagnosis is an integral component to accurate batch planning.


Resolving summer infertility

Get out of its way.  Minimise the impact of summer infertility by having the lactating, breeding and gestating sows in an ideal body condition.  Ensure there are no management or environmental failures over the summer months.  Note it gets cold overnight in the middle of summer – do not skimp on bedding.   If the farrowing rate falls – breed more females – gilts, culls and yes, if necessary, repeats (as a last resort).  Coping with summer infertility is about planned gilt pool management.

When is pig farming not about gilt pool management!


In the example table, the farm’s summer infertility problem historically starts mid July and extends to end of October.


Table 3.

Calculator to predict future gilt age and stage of preparation (webversion interactive)

The gilt pool and its selection of “extra” therefore can be predicted.


Having a lower farrowing rate in the summer is not a crime – it is normal.  The only purpose of recording the farrowing rate is to determine the number of sows to breed.   Do not make it determine profit and loss.


You and your genetic company

Discuss your summer infertility requirements with your genetic company.  Plan well ahead.  Biosecurity issues should specify the gilt input ages onto your farm.  In particular, PRRSv control.  If you use a live PRRSv vaccine, it is imperative to have had the vaccinated gilts stop excreting any virus before they enter the main herd.   For example if you purchase your replacement gilts around 60kg – they need to start arriving on your farm mid March – well before the expected summer infertility issues.


Post-summer breeding

After the summer period, the herd size will be too great for the winter breeding period.  Use this time to resolve parity issues through prudent culling programmes.  Do not over-breed in an attempt to “make up” the losses incurred because of poor planning in the spring and summer.


Effect of summer infertility on the herd output

There should be no impact on output


But if you drive the herd based on adult animals – by non productive days, pigs per sow per year, litters per sow per year for example, you will have lower incomes in the winter.   Then in the spring you will have overstocking from the excessive numbers bred to compensate for the summer infertility.  This will lead to increase incidence of diseases, reduced welfare and possibly breaking the law in terms of stocking densities.

As the spring progresses the herd size should increase, the output per farrowing place should have no change.  Even if the growth rate slows down as the finishing pig’s appetite drops in the hot summer – the batch just needs more time to get to the desired slaughter weight.  The building plan of the farm should accommodate this requirement – or the farm is forced to sell lighter pigs – increasing costs.


Table 4.

Impact of season on herd parameters (webversion interactive)


Impact of not coping with summer infertility

Empty farrowing places – empty grow finish pens – empty shackles: - Increased cost of production

Farr empty crate

Pig flow empty pen

Abattoir ch 1

Pic 2.  Empty farrowing places

Pic 3.  Empty finishing pens

Pic 4.  Empty shackles