Average parity of removed sows is a more stable measure of sow utilization than replacement rates or culling rates, yet there is little literature on the subject, says University of Minnesota swine veterinarian John Deen.
Calling it a much better management tool to measure sow attrition, average parity of removed sows is really a function of the farm's capability to choose the right sows, notes Deen.
“It measures the decision-making process of the person doing the culling. You need old sows to remove to get a higher level of retention. It's hard to have a removal parity of, say 4.0, if you hardly have any sows at parity 4. Most sows are young and removed at a young age. To increase the average, you have to change distribution of the herd.
“The simple decision to be made at the farm level is to retain sows as long as possible,” he maintains. “If we are arguing that the productivity of sows at parity 6 is so low that they are justified to be removed, then we should look at creating more robust breeding stock.”
There are many risk factors associated with sow removal, Deen continues. The presence of one of these factors in a herd does not necessarily mean a higher removal rate.
However, when many of the following factors are present, it is indicative of higher mortality risk.
Though often ignored, a larger risk for replacement rate is farrowing. As litters/sow increase, so does replacement rate, though average parity removed stays stable.
- Farrowing rate
Reproductive failure is the largest reason for removal, especially in low farrowing rate herds. The two strikes and you're out rule can almost guarantee a low parity removed average.
- Herd size
Mortality rates often increase with herd size.
Sows with more stillbirths are more likely to die subsequent to the stillbirths. The chance of mortality increases by 24% when one or more stillbirths occur.
- Stockman training
Although more specialized workers are hired by large farms, they may not have adequate time to pay attention to sows showing clinical symptoms.
- Gilt flow
The largest factor, when viewed on a week-by-week basis, is gilt availability. This is rarely recorded, but supply is feast or famine on many farms. This causes instability in the breeding target unless parity removed is varied.
Not all factors can be listed or included, Deen told veterinarians attending the 2002 Leman Swine Conference. The data available suggests that a major focus should be average parity removed. The only answer in addressing this variable is to decrease the number of young sows and gilts removed. This, in turn, reduces removal rates, increases average parity of the herd and increases the proportion of litters from older sows, he concludes.
“Of course, average parity at removal should always exceed the average parity of the herd,” he adds. “If not, the herd is in trouble and going downhill fast.”