Removing non-productive sows as well as introducing replacement animals is essential to maintaining breeding herd productivity at a constant level. High gilt-replacement costs also make it important to work to increase sow longevity and decrease attrition. Attending to these details may improve litter size and a sow’s lifetime productivity, and result in fewer non-productive days.

While breeding herd management and culling practices are part of an operation’s daily business, it’s still wise to ask: Why are sows being culled?

Numerous surveys can offer insight to the trends or factors that determine whether and how we can reduce the impact of culling young sows from the herd. For example, if we look at lameness as a reason to cull an animal, the estimates range from 9 percent to as much as 27 percent. The most recent National Animal Health Monitoring Study reports 15.2 percent of culling is due to lameness.

Other research suggests caution in using these numbers as absolute reasons why sows were culled or euthanized because the data show 23 percent of the culling causes were determined to be recorded inaccurately on the farm. 

Moreover, the surveys reflected a trend that young sows (less than parity 3) were often culled because of feet and leg problems and reproductive failure, while sows at parity 6 and older were culled mainly because of age and performance.

Structural Soundness and Longevity

As more research groups study and collect data on sow lameness, the industry’s overall understanding also expands. It’s well documented that sow claw and foot health is critical to improving sow well-being, maintaining sows in the herd for improved longevity and maximizing the economics of pork production.

University of Minnesota researchers report that specific claw lesions were associated with lameness and group housing in gestation. Their data show that lame sows were four times as likely to have cracks in the sidewall of a claw (hoof) as non-lame sows. Furthermore, sidewall cracks were 28 times more likely to occur in sows group-housed in gestation pens compared to sows housed in gestation stalls.

Additional Minnesota research found that lactation length, body condition and lameness were associated with increased shoulder ulcers. As lactation length increased, the odds of having shoulder ulcers increased 16 percent. 

Still, a greater impact was observed, where sows with a body-condition score of 2 or less had a 3.35-times greater risk of shoulder ulcers than sows with a body-condition score higher than 2. The greatest association with shoulder ulcers in the Minnesota data was with lameness. Lame sows had a 3.7-times greater risk of having shoulder ulcers than non-lame sows.

Nutrition, Reproduction and Culling

Nutritional management designed to optimize feed intake and intake patterns can improve breeding herd performance and reduce reproductive problems. A high daily lactation feed intake limits body weight loss and improves litter weight gain. Each kilogram (2.2 pounds) increase in feed intake reduces the probability of a prolonged wean-to-estrus interval by 42 percent. When young sows have poor daily lactation feed consumption and extended wean-to-estrus intervals, the practical outcome is to cull them for presumed reproductive failure. However, the repeatability of poor reproductive performance in young sows is actually lower than what's often suggested.

Another study showed that a 1-kg increase in daily feed consumption reduced the animal’s likelihood of being culled by 30 percent. Sows that consumed less than 7 pounds (3.2 kg) of feed on any day during the first two weeks of lactation (day 2 through 14) had a greater risk of being culled compared to sows that ate 7 pounds per day or more in those first two weeks. (See accompanying chart.) Sows that failed to consume feed on any given day during the first weeks of lactation had the greatest risk of being culled.  While simple, it appears that a significant key to reducing the chance of young sows being culled from the herd is to ensure that they are consuming enough feed.

The reproductive effects of inadequate lactation feed intake seem to be mediated, at least in part, through Lutalyse hormone secretion and embryo mortality. Low feed intake during lactation involves body tissue mobilization and can lead to excessive body weight loss, decreasing the sow’s longevity and reproductive performance. 

Sows with a body-condition score of 1 have a higher frequency of acyclic ovaries than sows with a score of 4.  In sows with low body-condition scores, it’s reasonable that some of the weight loss is due to increased protein loss. A 2003 study reported that losing more than 9 percent to 12 percent of body-protein-mass rapidly decreased ovarian function. Protein restriction throughout lactation alters circulating concentrations of somatrophic hormones and insulin late in lactation and negatively impacts post-weaning ovulation rate.

In the End

Food production costs will continue to demand greater efficiencies. It will become increasingly important to improve a sow’s lifetime productivity, as future goals will include producing nearly 60 pigs per year.

Research concludes that sow lameness is a significant culling factor, affecting the sow unit’s overall productivity and profitability. Research also shows improvements in sow herd management and nutrient supplementation may decrease the impact of claw lesions and lameness, and ultimately improve reproductive performance. 

No one factor will prevent or solve the sow lameness issue. Management, facility and nutritional factors all play a role, and it will take a coordinated effort to reduce the impact. As more information is gathered, the industry can more clearly define the exact practices that will prevent these inflammatory injuries.

Editor's note: Mark Wilson, a reproductive physiologist with Zinpro Corp., is located in Eden Prairie, Minn. You can e-mail him

Why We Cull Sows

Here are some common reasons why sows are culled from the breeding herd. Still, the real challenge is in getting an accurate assessment and record on the farm of why sows leave the herd.

Keep Lactation Diets Flowing

From farrowing through the first two weeks of lactation, a sow’s appetite and dietary consumption patterns matter. In a University of Minnesota study, sows that ate less than 7 pounds of feed a day faced increased culling chances. For any sow that skipped even one day, the chances increased even more.