Why sows leave the herd: Biological priorities and productivity

When it comes to sow productivity, culling and mortality issues, “the simple answer is there’s no simple answer,” John Deen, DVM, PhD, University of Minnesota swine epidemiologist, told Pig Health Today. “We need to identify better interventions and understand our herds in more detail.” That also means earlier interventions.

Sow mortality rates have been trending higher in recent years, some of which may be due to animal-welfare considerations and euthanasia protocols. A rise in pelvic organ prolapses (POP) also has added to the increase, which has demanded on-farm attention and prompted research directed at finding answers.

“It’s [POP] quite a distressing condition and very frustrating for people working on the farm,” Deen noted. “However, it’s not the major cause of sow mortality, and it seems to be quite distinct from other problems.”

Prioritizing life-cycle pathology

Deen would like to see more attention placed on noting what happens throughout the sow’s life cycle with the goal of understanding what causes may or may not lead to culling or mortality. Because culling reasons and mortality causes are recorded at the end of the sow’s life, it’s easy to miss many of the contributing factors. The assessment is subjective, so you end with what can be described as a barn worker’s best guess, Deen noted.

In the farrowing house, management relies on sow cards to identify which sows are most likely to fail to perform. “My argument is that those sows don’t perform well because of a pathology that we may see in historically poor performance,” Deen said.

By looking more closely at the sow and the pathology along the way, it could be any number of insults that stresses a sow. It could be an inflammatory process that reduces ovarian activity or lameness that reduces lactational feed intake and begins a body-condition spiral downward.

Diseases, whether bacterial or viral in nature, such as swine influenza virus-A or porcine reproductive and respiratory syndrome, present another challenge that the sow must cope with, and sometimes it’s unsuccessful.

A multitude of factors

Sow diets often rise to the top of the list, but dietary issues can be caused by a nutrient deficiency or as a result of sows not eating enough. Deen noted the latter needs more attention. Bottom line, today’s highly prolific sows sacrifice their self-protection in order to maintain milk production for the litter’s survivability. There can be a combination of factors in the farrowing crate where sows stop eating. Sometimes the appetite just isn’t big enough.

As Deen emphasized, if sows don’t eat enough to meet their high metabolic requirements during lactation, they may not come back into heat. If they do return to estrus, they often fall apart.

“They either become infertile, die, are subject to euthanasia or end up on a truck,” he said. “We need to provide extra care for the sows — to recognize when they cannot cope with the insults that they have in front of them, whether it be infections, heat or lameness.”

Increasingly, today’s sow simply cannot adjust as quickly as past genetics to reproduction and lactation expectations. “If we look at which sows die in the face of some of these insults, it’s more likely to be lactating sows that are under more metabolic pressure,” Deen said.

Successful and unsuccessful culls

Just as knowing more about what causes sow mortality within a herd, it’s equally important to understand why an animal is culled. Again, monitoring and recording challenges that a breeding female encounters along the way will tell you more than jotting down a culling reason as the animal is loaded onto the truck.

Deen emphasized that there are successful and unsuccessful culls. “A successful cull is meeting the expectation of the gilt at the time of entry,” he said. “In most herds that would be to produce six good litters, and at the end of those litters, being a healthy animal that gets onto the truck and receives a full-value price as a culled sow.”

However, a low proportion of the total gilts that enter the breeding herd actually end up meeting those expectations. It can be as low as 10% to 15%, Deen noted, which means there is a lot of unsuccessful culling underway.

Certainly, there is an economic motivation to improve sow culling and mortality rates, but there is an animal-welfare component to it as well. “There’s usually an agonal [painful] process in the sow before it dies,” Deen noted.  And younger and compromised sows produce progeny with poorer performance.

“We need to understand the true cost of mortality,” he added. “Once we start adding up all these factors and outcomes, there’s a huge opportunity to increase productivity and especially the quality of progeny.”