Pigs per sow per year (PSY)

 

Pigs per sow per year (PSY) is an overused parameter of pig production and is used to indicate “good” production, but the number is heavily favoured towards larger farms who wean early.   Unfortunately, pigs per sow per year provides no indication of profitability, which is the real measure of success.

 

The adult herd is not where pig production should be measured as they are not a major feature in the farm cost structure.   A farmer who is not so efficient at breeding can still be extremely successful if finishing costs are well managed.  For example any farmer who concentrates on finisher feeder management will always be more profitable than a farmer which is merely good at breeding.

 

Why should pig production avoid using the “sow” as a focus point and in particular “pigs per sow per year (PSY)”?

·        The variability in the definition of a “herd: and  “sow” both between countries and even between farms

·        The measure cannot be used to compare farms of difference herd size

·        The actual number of “sows” is easily open to fudging by farm staff

·        The sow number is susceptible to variation over the year whereas the total output is fixed

·        Variation occurs between different weaning ages

·        Variation in the definition of the term “pig”

·        The measure provides no indication of the actual number of full value pigs or kg of meat produced

·        The measure provides no description of health controls

·        The measure provides no indication of the cost of production

·        The measure has no specific impact on profitability.

·        Pig production systems need to move towards reducing variability.  Concentrating on PSY actually will increase the variability within the system.

 

Definition of “pigs”

When looking at any “pigs” per sow per year analysis, it is vital to understand exactly the definition of the term “pigs”.  Are the figures referring to total born “pigs”, numbers of “pigs” weaned or “pigs” sold at finishing.  While none of these are actually the end product of pig farming – which is weight of pig meat paid for – they can be useful target monitors.

 

Effect of “pigs” definition on PSY

Unless specifically mentioned, in this paper a standard farm is described:

The farm practices weekly batches with 20 farrowing places per batch.

The farm weans 11 pigs per farrowing place

The farrowing rate (FR%) is determined at the winter time herd size (87% FR).

The total born is calculated at 30% more than numbers weaned.

The farm practices 4 week weaning (average 27 days old).

The finishing rate is calculated at 95%. (5% post-weaning mortality).

 

“Pigs” definition

Total born

Numbers weaned

Pigs sold

PSY

34.0

26.1

24.8

In the rest of this paper “pigs” will be defined as the numbers weaned.  Obviously this then immediately ignores the finishing herd and the quantity of pig meat sold from the farm.  The point when the farm actually gets paid for its efforts.

 

PSY and farrowing rate

As the farrowing rate of a farm falls, the number of sows needed to reach the breeding target increases, thus a decrease in PSY.  It is obviously important to achieve a satisfactory farrowing rate.  Emphasizing the farrowing rate and PSY can lead farms to lose focus on filling all the farrowing places.  Having a 95% farrowing rate and 28 PSY sounds great – but each empty farrowing place costs 800kg lost pig meat!  Only once the farrowing places are all filled – 52 weeks of the year, can producers start boasting about their PSY.

 

Impact of farrowing rate% and PSY (20 batch farrowing places)

Farrowing rate

70

75

80

85

90

PSY

24.1

24.8

25.4

25.8

26.1

 

Herd size and farrowing rate impacts on PSY

Larger herds can be more precise regarding the actual number of sows required to meet the breeding target for any set farrowing rate.

For example a family farm with 10 sows a week batch (240 sow unit) the same number of sows is required to be bred between 83 and 91% farrowing rate.

Whereas a 100 sows a week batch (2400 sow unit), each unit of farrowing rate equates to an individual sow.

 

Thus the PSY will increase with herd size irrespective of any other change in production.

Thus PSY cannot be used to compare farms which are different in “herd” size.

 

Herd size and farrowing rate impact on PSY

Herd size

10

20

30

40

50

60

FR %

70

23.8

24.1

24.2

24.1

24.2

24.2

75

24.4

24.8

24.9

24.8

24.8

24.9

80

25.1

25.4

25.3

25.4

25.4

25.4

85

25.8

25.8

25.8

25.8

25.9

25.9

90

25.8

26.1

26.2

26.3

26.3

26.4

95

26.5

26.5

26.7

26.7

26.8

26.7

Herd size is determined by the number of batch farrowing places available.

 

Seasonality and PSY

There are times when the farrowing rate changes predictably.   Thus the PSY will naturally change throughout the year.  In the Northern hemisphere the drop in farrowing rate is around 5-10% and this drop may last 3 months.  In the Southern hemisphere the farrowing rate drop may be 15%, but the duration is only 6 weeks.

 

 The farm therefore has two options:

1.     Vary the size of the sow herd over the year to stablise the kg meat output

2.     Keep the same sow herd size and allow the kg meat output to vary

Clearly the most profitable option is to vary the sow herd.  The sow is only 20% of the cost of production.   Therefore the PSY will also vary over the year – with a maximum taken at some time when the herd is the smallest- in late winter – and take the annual meat production.

 

PSY with season

If our example farm is in the northern hemisphere and seasonal variations result in the farrowing rate minimized in the later summer to 74% whereas in the summer a farrowing rate of 87% is enjoyed.

 

The real PSY produced over the year varies

Season

Winter

Summer

PSY

26.1

24.4

 

Thus when comparing two farm’s PSY it is vital to know when the calculation was made and where on the planet the farms are situated!

 

Weaning age

Around the world weaning age varies. In the EU weaning has to be above 3 weeks.  However, an alteration in weaning age alters the number of sows required to produce piglets. Thus the PSY will increase with a decrease in weaning age.  Thus European farms will naturally have a lower PSY than farms practicing 3 week weaning.  Thus a drive towards PSY leads to a reduction in weaning age – which is not necessarily good for production.  Many farms can have increased profits once the farm moves to 4 week rather than 3 week weaning.  Note reducing weaning age makes the “farrowing place” not the sow more productive.  But, it drives an increase in nursery costs.   The move towards wean to finish systems is enhanced by increasing the weaning age – but this will reduce PSY.  But if it increases profit why worry about the PSY?

 

Impact of weaning age on PSY

Weaning age (weeks)

3

4

PSY

27.4

26.1

 

Number of pigs weaned per batch farrowing place

The number of pigs weaned per batch farrowing place has a tremendous impact on PSY.

 

Number of pigs weaned per batch farrowing place on PSY

Pigs weaned per batch farrowing place

9.5

10

10.5

11

PSY

22.6

23.7

24.9

26.1

 

Batch length

Batch length has no specific impact on PSY.  Apparent impacts are associated with weaning ages.

 

How many “sows” are there?

Definition of herd size

The definition of herd size varies from country to country and even around a country – making comparisons between the PSY of two farms extremely difficult.

 

Alternative definition of herd size using the batch farrowing place

It is possible to define the “minimum” herd size required to ensure the all the batch farrowing places are filled.

(Number of batch farrowing places) +

(Number of batch farrowing places/farrowing rate *  number of batch times to pregnancy)

 + (Number of batch farrowing places* number of remaining batch times to farrow)

 

For example using our example farm:

20 batch farrowing places and one week batch with 4 week weaning:

5 batches of farrowing places = 5*20 = 100 sows

Pregnancy check at 6 weeks and farrowing rate 87% = (roundup (20/0.87))*6 = 23*6 = 138 sows

Rest of gestation = 16 weeks minus 6 weeks = 10 weeks*batch farrowing places = 200 sows

Thus the minimum herd size for this farm would be (100+138+200) = 438 sows.

 

The “gilt”

When does the gilt actually enter the farm and become part of the herd.  How do we accommodate gilts which are “extra” to  those which are not selected and even those which are part of the “insurance” to ensure that the batch breeding target is met. Thus a drive to maximize PSY will minimize the “insurance” policy of gilt numbers – which if the breeding target is not met, this results in 800kg of pig meat not sold for each empty batch farrowing place.

 

Role of the “cull” sow

Cull sows can be a vital part of stabilization of pig flow.   Delaying culling until breeding targets or pregnancy targets are met can be a vital component of reducing variability on pig farms.  But retaining cull sows decreases PSY but maximizes output!  

Many farms are extremely careless about time of culling.  Is the cull sow “removed” from the records on the day the decision is made or when she leaves the farm?  The drive to increase PSY leads stockpeople with little option but to “record” the cull as soon as possible – but the sow may still be on the farm eating feed!  The need to collect sufficient sows to fill a transporter puts the smaller farmer at a disadvantage with regards to PSY compared to a larger farm.

 

Impact of changes in managing the gilt or cull sow on PSY

Gilt replacement rate is calculated at 40%

Cull management

PSY

Culls removed from the records immediately

26.1

Culls retained a week

25.9

Culls retained 6 weeks

25.0

 

Conclusions

The sow is not a major part of the farm cost structure. The major cost of keeping a sow on a farm is associated with the food she eats – which on most farms is about 1.1 tonnes per sow per year.  Obviously the number of finishing pigs this equates to depends on the value of the pig – but around 5 pigs per year taken to a 110 kg finishing weight will pay for the sow’s costs.  The sow is significant amounting to around 20% of the cost of production, but there is still an addition 80% that needs to be managed.

 

Pigs per sow per year should not be used as a benchmark of pig production because the result is subject to variables which farm’s stockpeople can easily manipulate and subject to the natural forces of nature over the year.

 

Average variation in pigs per sow per year which can be expected:

Variable

Typical reduction in PSY

Weaning age changes from 3 to 4 weeks

1 pig

Farrowing rate changes from 85 to 70%

2 pigs

Herd size from 2500 sows to 250 sows

0.3 pigs

Seasonality from winter to summer

1 pig

1 less pig weaned per batch farrowing place

2.5 pigs

Retaining culling sows for 6 weeks

1 pig

 

If pigs per sow per year is defined regarding the weaned pig, it offers no indication of the success of the finishing herd.

 

Pigs per sow per year provides no indication of profitability, which is the real measure of success.

 

PSY calculator