by Megan Schnur, DVM
Carthage Veterinary Service, Ltd.
Carthage, Illinois

Sometimes it’s difficult to determine whether pigs were actually stillborns or if they were born alive and died shortly afterward. One way to tell the difference is by examining the lungs for signs of aeration. For instance, if the lungs are pink and inflated, that indicates respiration occurred and the pig was born alive. You can also tell by removing the lungs and placing them in water. If the lungs float, the pig was born alive.

In contrast, a stillborn pig may appear to be fully developed but will show no signs of respiration. Upon gross examination, the lungs appear dark and consolidated.

Where to start

Expected target levels for stillborn pigs vary with management practices. In general, a stillborn rate of 3% to 5% is acceptable in modern production systems. When the incidence of stillborns runs higher, the first step toward resolving the problem is a review of production records to determine parity distribution and gestation length. Older parity animals, for instance, have a greater likelihood of delivering stillborn pigs. A reduced gestation period or one exceeding 120 days is another cause for investigation because it could indicate a disease or feed problem.

Visiting the farm to review management practices can also yield additional clues about the increased incidence of stillborns. Pay close attention to sow nutrition, induction practices, farrowing attendance and environmental factors that can stress sows.

You’ll also want to make sure feed-box settings are appropriate for the body condition of sows in late gestation. Sows that are overfed and overweight are more likely to have difficulty farrowing, especially in warm weather, resulting in mortalities during farrowing.

In many production systems, it’s common practice to use prostaglandins to increase the number of farrowings that occur during normal working hours. However, if they’re administered prematurely during gestation, they can actually increase the number of weak and stillborn piglets.

Use attendants

In numerous studies, 24-hour farrowing attendance has been shown to significantly reduce the incidence of stillborns. It’s best to have an experienced, attentive person present to keep a close eye on sows, especially those that are older, at higher risk and that may need assistance. This not only reduces the interval between successive piglets, it can minimise the potentially adverse impact of large litters and/or piglet size, piglet birth order and farrowing complications.

Environmental observations that can contribute to stillborns include carbon monoxide exposure — for example, from faulty gas heaters — and excessive ambient temperatures that lead to heat stress.

Infectious versus non-infectious

To determine whether the root cause of stillborns is an infectious agent, you’ll need to obtain a thorough history of the herd. Have there been high numbers of sows off feed and/or with high fevers? Is the prevalence of abortions elevated? Is there an increase in small, weak-born piglets or mummies? Are the sows farrowing early?

If the answers to these questions are “no,” the focus should be on non-infectious causes. If the answers are “yes,” then a more extensive investigation is warranted through collaboration with a veterinarian who can collect diagnostic samples for testing, make a diagnosis and help producers implement appropriate interventions.

There are several reproductive pathogens capable of causing an elevation in the incidence of stillborns. The first and perhaps most widely recognised infectious agent is porcine reproductive and respiratory syndrome (PRRS). A herd infected with PRRS will generally show an increase in abortions, which leads to an increase in stillborns, mummies and a reduction in total born.

There’s a long list of infectious agents that can cause systemic illness — such as a high fever or that cause sows to go off feed — and also result in reproductive failure. These include influenza and erysipelas.

Certain other infectious agents, such as parvovirus, tend to present themselves in first-parity animals. Typically, there’s an increase in stillborns following the delivery of variably sized mummies. Other reproductive infectious agents in the US that lead to an increase in stillborns include leptospirosis, porcine circovirus type 1 and enteroviruses.

Pinpointing the cause of stillborns can be challenging because the list of possible causes is long. However, it’s well worth the effort if we can minimise the incidence and the resulting economic losses.