Its calculation is based on two variables: the average parity at removal and the average number of weaned piglets in each parity.
The purpose of this parameter is to inform about the production of our sows that have either been culled on the farm, die on it or have been sold to a slaughterhouse for whatever reason. Undoubtedly we all want that when a sow, for one reason or another, leaves our farm, it has been able to previously show its highest production level. The problem is that sometimes there are other indices that dazzle us, such as piglets weaned/sow/year, and for that reason the productive history of a sow throughout its stretch on the farm goes more unnoticed. But we must not forget that the term depreciation is as applicable to the sows as to the farm itself, and the index "piglets weaned per sow lifetime" is a good indicator for deepening the knowledge regarding sow depreciation.
To illustrate this production concept, we are taking as an example 2 farms that may seem quite similar to each other beforehand:
Table 1. Main production indices on farms A and B. Year 2017.
|Farm A||Farm B|
|Piglets weaned /sow/year||30.3||30.1|
|Average piglets weaned /sow||12.7||12.0|
|Farrowing rate (%)||88.9||87.9|
|Lactation length (days)||24.9||20.8|
|Average sow age (parity)||2.5||2.8|
As shown in Table 1, both farms have very similar production levels (piglets/weaned/sow/year). Although the average number of piglets weaned per sow is higher on farm A, farm B makes up for this lack, achieving a higher farrowing index due to a shorter lactation length.
Looking closer on how the productive life of the sows removed on both farms for the specific period was, some small variations can be seen, which at the end will make a big difference between both farms.
Table 2. Main traits of the sows dead/destroyed at the farm on farms A and B. Year 2017.
|Farm A||Farm B|
|Average age at death (parity)||2.1||3.0|
|Average piglets weaned /dead sow/farrowing||11.10||9.62|
|Average piglets weaned /dead sow||23.31||28.86|
The main difference seen between both farms is the average age (age as parity) at culling. Farm B has an average of almost one farrowing more than farm A. This difference balances out the lower value on farm B regarding the average number of weaned piglets/sow/farrowing, and makes the average value of weaned piglets per dead sow be higher on farm B. We must bear in mind that the average culled sow on farm B has produced 5.55 piglets more than on farm A on the basis of having had a longer productive life.
Table 3. Main characteristics of the sows sold on farms A and B. Year 2017.
|Farm A||Farm B|
|Average age at sale (parity)||4.5||5.1|
|Average piglets weaned /sold sow/farrowing||12.07||11.78|
|Average piglets weaned /sold sow||54.32||60.08|
In the case of the sows sent to slaughter, the situation is similar to the previous case. In this case, the difference between the average age of the sows sold on both farms is lower (0.6 farrowings), although the higher number of piglets weaned on farm B makes that the difference between both farms with respect to the piglets weaned per sold sow shows a similar value to that of the dead sows.
That said, what would be the performance on farm A if the productive life of its sows was similar to those on farm B? Or, in other words, what would be the production level with a higher average age at removal?
Table 4. Estimated performance on farm A if sow longevity was longer (as on farm B). Year 2017.
|Farm A (real)||Farm A (with removal age as on farm B)|
|Average age at removal (parity)||4.2||4.9|
|Average piglets weaned /removed sow/farrowing||11.98||11.98|
|Average piglets weaned /removed sow||50.32||58.70|
In this scenario, we can see that the sows would greatly benefit from their greater potential because of a longer productive life (which implies a greater number of farrowings at removal) together with a higher productivity (referred to as the average number of weaned piglets/removed sow). Specifically, the difference would be 8.38 piglets per sow at removal between one scenario and the other.
In short, we should not always allow ourselves to be carried away by certain productive indices that overcloud some aspects on the farm. If we want to have a broad knowledge of our farms, we must know some indices that are usually more concealed, but that undoubtedly give us valuable information on sow performance, or as in this case, information about the culled sows.