The problem is with pigs per sow space.

By John Deen and Sukumaran S Anil, University of Minnesota

Here is a simple question: What is the difference between pigs per sow per year and pigs per sow space per year? This is a more complicated question than you might think, but it is an important question, particularly as we look at sow longevity. Sows are removed from the herd due to death, or due to culling under three scenarios:

• The sow is immediately replaced with a cycling gilt that comes into estrus as the sow is removed. This may be the case when a sow is removed at weaning and a prepared gilt is ready to replace the sow. In some ways, this is the perfect pass within the sow space, and the only thing we have to worry about is that the performance of the replacement gilt equals or exceeds that of the sow. The gilt inventory is synchronized with the culling behavior.


• The sow is immediately replaced with a cycling gilt whose estrus is not synchronized with removal. Therefore, there is, on average, half of 21 days to breed the animal. This can be considered a pretty good pass, as the makeup time is easily identified.


• The sow is not immediately replaced. This may be due to the fact that the breeding group has already been established and no further sows can enter the herd at that time, or it may simply be that there are no gilts available. This can be considered the dropped pass, where the sow space remains empty for some time.

There are many cases where a sow was removed and the space was left empty for extended times. Such behavior improves pigs per sow per year but decreases pigs per sow space per year.
- John Deen and Sukumaran S Anil

These scenarios are closely linked with the type of culling seen in the herd. More often than not, sows culled at weaning have ready replacements. However, sows culled at later times are often not readily replaced, and this type of culling has a discreet effect upon the functional capacity of the sow herd.

There is, in our opinion, a big problem in emphasizing pigs per sow per year instead of pigs per sow space per year when we examine culling strategies. Here is the simple question: If a sow was removed due to low expected performance, should we differentiate that decision based on whether or not there is a replacement ready and available?

There are many cases where a sow was removed and the space was left empty for extended times. Such behavior improves pigs per sow per year but decreases pigs per sow space per year.

In economic terms, the basic question is whether sows should be retained if there is no replacement. We believe they should be, if there is not a welfare concern. In these cases, the sow can easily cover her feed costs, even with low productivity.

Figure 1 shows the relationship of pigs per mated female per year and pigs per sow space per year across 14 herds for 2008. There is a generalized relationship between pigs per mated female per year and pigs per sow space per year, but it is far from a simple relationship. It also looks as if once the farm reaches a plateau, there seems to be a lessened capability to produce pigs per sow space.

This review shows there is real variation in sow farm productivity that may not be explained simply by pigs per sow per year. In the future, producers should look more closely at the capability to use the facilities they have. There is real variation in facility utilization over the seasons as well, and these factors should be examined in further detail.

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Editor’s Note: John Deen, DVM PhD, is an Associate Professor at the University of Minnesota, and Sukumaran S Anil, DVM PhD, is a Research Associate at the University of Minnesota. To contact them, e-mail: deenx003@umn.edu or sukum001@umn.edu

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