Making a decision to cull a sow


The decision to cull a sow is one of the most important management decisions you can make. 
The first question should be:

“Is the welfare of the sow compromised?”

If so then the sow must be hospitalized, destroyed or culled immediately.


However, if the sow is not compromised – the second question should be:

“Do I have a pregnant gilt which will farrow in the same batch to replace this sow?”

– if not you cannot cull the sow.


If I fail to cull properly what does this cost the farm?

Farr empty crate

Pig flow empty pen

Abattoir ch 1

Empty farrowing places

Empty finishing pens

Empty shackles


What options are there in the timing of culling?

On many farms sows are culled at the point of weaning, perhaps the decision is made even during lactation.  But what guarantee does this decision give you?     Very little!


There are three major times when culling should be considered:


The cost of keeping an extra sow to ensure that the breeding target and the pregnancy target are met is discussed in table 1.  These costs are small compared with the $280 costs ($1 per kg deadweight costs) incurred with nine or ten empty shackle spaces in the abattoir.  However, if producers are worried even about these small costs, it can be balanced by reducing the gestation sow intake by only 150g a day.  And, considering many farms suffer from overweight sows in gestation, this reduction would probably enhance lactation feed intake with subsequent benefits in wean to service intervals and future litter sizes. What is especially frustrating is when breeding targets are not met but cull sows are kept for weeks until there is a truck load.  

These costs can be further investigated for specific farms using the linked spreadsheet


One option is to keep the sow to be culled past the end of the breeding week

Retaining cull sows until their pregnancy check is an option, but it is essential that pregnancy checking is accurate. 

Ideally use a real-time ultrasound and then wait until day 28 of pregnancy.  Before this too many mistakes are made.  After day 36, if there are any doubts, it will be difficult to perform a second check before an “open” sow shows her third post-weaning cycle.  However, at 28 days it is vital to note the presence of the embryo (arrowed) as well as the “hole” of the foetal amnion and allantois.

24 days gestation


Table 1

The financial impact of the time of culling



Time of culling:

What can I guarantee?

Number of sows bred

Number of sows pregnant

Number of sows which farrow

Lactation or weaning




End of breeding week




24 days post-weaning




28 days pregnancy check




At farrowing




transport pig k1

Repro AI pack19

24 days gestation

Farrowing outdoor au

What are the costs estimates?   Example: a family farm with a batch of 10 sows farrowing a week:

Cost of keeping the sow to the point of culling

Using kg dry sow feed equivalents

117 kg

155 kg

450 kg


AI costs only. Sows retained one week post-weaning to regress  mammary glands and antibiotic withdrawal times

(5+28-7) days + AI costs

(5+115-7) days + AI costs

Feed  costs at $150 per tonne dry sow feed:




The number pregnant is obviously dependent on the operator’s accuracy at pregnancy diagnosis.

Sow costs:  As sows eats 2.5kg a day and this represents 65% of total costs of keeping a sow.  There are two inseminations with a value around $5 per AI.

What is the loss of income? It is assumed that the culled sow was required to fill a farrowing place.

Assuming 10 weaned and each pig finishes with 80kg deadweight – this results in 800 kg pig meat not sold.

At $1.00 per kg income – this is $800 per empty farrowing place of costs.

As these finishing pigs never existed, they would not have eaten. 

BUT - There are still the fixed costs to be paid - $280 per batch ($800*35%) not including any profit to be made


There still needs to be a culling programme

Sows still need to be culled, the premise of retaining a sow for later culling is to provide options for the farm: not to stop culling and replacement of old sows.


Sows kept until the end of the breeding week

When we wean on a Thursday, the first day of the new batch should be Friday.  If we breed all possible sows over the breeding week and cull on the following Friday, we have at least made it more likely that the breeding target is met.  In addition, the sow’s udder has regressed and even possibly some lameness/stiffness issues have been corrected, making the animal more valuable at slaughter.

Note, never mate a lame sow with a boar, and only ever mate by AI.

Note that with the addition of antibiotics to AI semen, there may be a withdrawal time.  This needs to be taken into consideration with regard to the costings.

Sows kept until pregnancy checking completed

If we retain the sow until pregnancy check, the concept to ensure that sufficient sows are pregnant (presumed) before any actual culling takes place.  If sufficient sows are pregnant (with full bellies of piglets) do not even bother to pregnancy check the sow marked for culling.  The duly culled pregnant sow will not be recognized at slaughter, as 28 day foetuses are extremely small.    Additional benefits include recovery from weaning and lactation with the possibility of additional weight recovery.

Repro foetus 25 days

Real size 25 mm

A possible secondary advantage of these pregnant animals is that through pharmacological abortion, they may even be used to fill in holes in the breeding programme following a review by the farm breeding team.

Mating a sow also decreases her food conversion ratio, assisting the conversion of feed into pig meat during the time before actual slaughter.


Sows culled until farrowing

It is not contemplated that extra sows are kept to the point of farrowing.  However, it is always assumed that the number of pregnant sows that enter the farrowing pool will equal 110% of available farrowing places – thus for a 10 sow batch farm – 11 pregnant sows will enter the farrowing pool.  The aim of breeding is to breed 12 sows again by weaning 100 piglets and 10 sows, not to just farrow 10 sows!

If you retain all bred sows, in excess of 110%, to the point of farrowing, serious welfare problems will arise associated with the excessive overstocking in the piglets, growers and finishing area.


Some sows need to be culled

Even sows or gilts which return once should be culled if possible.  At least they should be given a natural service in conjunction with the first/or two artificial inseminations.

Especially sows which kill piglets and have low numbers weaned.


Example of sows which should be culled

Foot extreme bush foot

Outdoor breeding gilt moving 5

Severe bush foot in a sow – despite treatment the sow is severely lame  this animal needs to be culled/euthanased on the farm

A sow has returned for a second time – culling is the only economic option – the reproductive success rate is appallingly low – less than 50%


Which sows should not be automatically culled?


OK, if I am going to change my culling programme, when should decisions be made on which sows to cull?


This should be done at 4 points during the breed to breed cycle (4 week weaning is assumed).



When the batch fails to fill all the farrowing places, you must add gilts to the system.

The farm’s team already knows that there is going to be a need for extra gilts in 5 weeks time (4 week weaning).

If it is impossible to hit the breeding target, there is absolutely no excuse to again fail to reach the breeding target in 20 weeks time (when this batch group farrows, weans and then breeds again).  When the farrowing group is going to fail to reach breeding target, the future gilts are around 20 kg live-weight.  It is extremely disappointing when farm reproductive records are reviewed that the same mistake occurs every 4.5 months. 

If a mistake occurs in this batch, accept it.  The farm team has 20 weeks to correct the mistake and ensure that it must not happen again.



At the point of breeding, if the breeding target is missed, future gilts for the next time this batch are going to be bred need to be prepared; they are currently 35 kg in weight.


Pregnancy diagnosis

At the time of pregnancy diagnosis, the farm knows what the likely number of sows which will farrow in this batch.  The future gilts required to mate with this batch are now 15 weeks old – around 60 kg.


Between 10 to 11 weeks of gestation

All sows around weeks 10 to 11 should be carefully examined by the farm manager and the breeding supervisors.  Any sow which is deemed to be suboptimal should be marked for culling.  The selected gilts needs to be added to the pool so they will be in 2nd, 3rd or 4th oestrus when this batch is being bred again. 


Let’s assume the gilts enter the breeding pool when the future batch is at around 100 kg, are introduced to a boar, cycles within 5 days and then cycles twice before being bred (mated on her 3rd heat into the breeding pool), this is 7 weeks post-introduction into the breeding pool.


Therefore, the gilt needs to enter the breeding pool at 15 weeks of gestation for this batch.

(1 week wean to service)+(4 weeks lactation)+(Last 2 weeks of gestation) = 7 weeks

Reviewing the sows at 10-11 weeks of gestation allows the farm four weeks to arrange delivery of the future breeding gilt to the farm.


Note that if the farm wishes to control PRRSv or other pathogens, extra time (minimum 6 weeks) should be added for isolation and acclimatization. In this case review of the gestation sows must occur around week 8 of gestation.  Gilt introduction programmes


What should I look for at 10 to 11 weeks of gestation?

  1. Ensure all to be retained sows are pregnant – visual assessment
  2. Ensure that all future sows are sound on all their feet
  3. Ensure that all future sows have no visual gross abnormalities to their udders
  4. Review the sow’s performance – age, # weaned, # total born (not born alive), returns.


Pregnant sow

feet sow k1

Ensure the sow is pregnant – this sow is close to farrowing

Ensure the sow’s feet are sound – her feed is overgrown

Mammary actinomycosis 03 sw

Breeding area us Brad

Ensure there are no abnormalities to the udder – note the chronic mastitis

Review sow’s reproductive performance – especially numbers weaned


This system of gilt requirements can also be programmed to your farm’s particular circumstances.  Review culling programme and gilt preparation spreadsheet.


Making culling decisions about a sow during lactation or at weaning is not logical.  The farm health team has allowed no chance for the breeding team to ensure sufficient gilts are available 52 weeks of the year.


Summary of gilt introduction timing considering various sow culling options

Sow culling option

Gilt weight kg

Sow culling/Gilt introduction graphic assuming 4 week weaning

Weaning age




110 or




130 or




130 or



Pregnancy check

(28 days)




Sow gestation check between 8 and 15 weeks

Depends on biosecurity requirements

Enlarge graphic


On a small point, note that the number of gilts required to fill a cull sows place does not equal one to one.  The gilts expected farrowing rate is only 75% which is lower than the expected farrowing rate of 85% for a mature sow.  Ensuring enough females have been bred this batch.   Thus to replace 100 sows require 115 gilts.


If I change my culling programme, how many sows should be farrowed?

The obvious minimum answer is the number of farrowing places.  But note the term is minimal.  To achieve this there should always be sufficient pregnant sows post 6 weeks of gestation to fill 110% of farrowing places, sows to farrow – per batch.

“But if the example farm has 10 farrowing places: there is no room for 11 sows to farrow?”

The farm can fill 110% farrowing place capacity adopting the following concept:  Several batches a year will present with 11 sows pregnant in week 16 of gestation.  Load the farrowing places with 10 pregnant sows as normal around 110 days of gestation.  Leave the sow mated last in the breeding batch in the gestation area.  When about the third sow farrows (not a 1st or 2nd parity sow) allow the piglets to suckle colostrum from their mum for about 12 hours, and then wean the sow.  Distribute the piglets to the previously 2 farrowed sows.  The weaned sow is moved into the next breeding batch.  The sow which was retained in the gestation area is moved into the empty farrowing place.  The piglets are  used to even up litters especially to gilts and low litter sows.  Note with tight breeding schedules, farrowing should also be tight, making this manipulation fairly easy.   It is obviously vital to ensure that the sow which stays in the gestation area does not farrow there.


This method boosts the farrowing output which is the purpose anyway, and maintains all-in/all-out in the farrowing area and weaning age distribution.


Programming more than 110% farrowing place capacity results in welfare issues in the piglets and generally causes the farm team to cheat on all-in/all-out or induce more variation in weaning age.


But, changing my culling programme is going to decrease my performance

Changing the culling programme is going to:

1.       Increase non-productive days (NPD).  Who cares?  The number one priority is filling each and every farrowing place 52 weeks a year.  Once this happens then the farm can use tools like NPD to try and trim costs.

2.       Decrease my pigs/sow/year.  Who cares?  You are paid for kg sold not for pigs/sow/year.  The only way to increase pigs/sow/year is to fill all farrowing places and then to wean more pigs per farrowing place.  No production parameter should be used which is a measure of “per sow”.  The herd size does not determine pig flow.

3.        Increase the sow herd.  Who cares?  There may be an impact on the environmental impact calculations on the farm regarding pig units.  Increasing the herd only increases the sow feed costs.  But if less feed is fed per sow or a lower sow feed cost is negotiated these costs disappear.  The sow herd should fluctuate over the year anyway, otherwise kilogram output fluctuates over the year.


Impact of season on herd size and output – customisable spreadsheet

On a 10 sow a week farm, selling 9.5 pigs per farrowing place at 80 kg deadweight

If the output cannot vary = 7600 kg per batch or 395200 kg per year

Herd size in winter 239 sows and gilts, in the summer 257 sows and gilts

If the herd size cannot vary = 239 sows, output from summer breeding is reduced to 6080 kg per batch  or 364800 kg per year or a loss of 456 pigs per year.

Significant increase in costs per kg sold

4.       Reduce my farrowing rate?  Manipulation of the figures can actually “increase” the farrowing rate.  The farrowing rate is only a guide to the required minimum breeding target – it is not a guide to profit and loss.  The farm is not paid more for having a “better” or “higher” farrowing rate. It is important that the farm only count those females bred which are intended to farrow not those also bred as part of the culling pool.


The pig industry must change towards farming for profit rather than paper performance targets