Unlike the severe reproductive losses associated with the first case of PRRS (porcine reproductive and respiratory syndrome), and the very high grow-finish mortality seen with porcine circovirus Type 2, sow mortality can be a slow, insidious problem.

As the swine industry evolved, sow mortality rates gradually increased. Concern with increasing sow deaths heightened in the mid- to late-1990s. Sow loss in several herds climbed from target levels of 3-5% to 10-20%.

Investigations found problems often to be multi-factorial and frustrating to try and isolate a primary cause.

Following are three case studies of herds with high sow mortality.

Case Study No. 1

A 750-sow, farrow-to-finish, one-site herd in Indiana flows pigs all-in, all-out through rooms. This PRRS-positive herd has had only one period with a slight increase in abortions in the past six years. The herd consists of York-Landrace females produced internally. Gestation facilities include a combination of stalls and pens, with most sows gestated in stalls.

In 2001, sow mortality was 9.7%. The death rate decreased in 2002 to 6% with no specific changes. However, in 2003, 11.1% of the sows died. Because of the work reported with antibiotics in lactation diets decreasing sow mortality, chlortetracycline was added to those diets. Several sows and gilts died during or after difficulty farrowing.

A genetic change was made and more effort placed on maternal traits in the selection of replacement animals. An improved gilt development program ensured a high percentage of gilts had heat-no-serve dates assuring better size at the time of farrowing.

Sow mortality for 2005, 2006 and 2007 has been much improved at 3.7%, 4.9% and 3.1%, respectively. It's likely this herd's high sow mortality was related to several factors linked to genetics and gilt development.

In addition, personnel changes contributed to the improvement. We are considering removing the lactation antibiotic and monitoring for any subsequent change in sow mortality.

Case Study No. 2

A 600-sow, breed-to-wean herd decided to change genetic sources. The sow herd is positive to PRRS virus and Mycoplasmal pneumonia. High-health gilts were purchased. They were isolated off-site and unsuccessfully inoculated with the farm's PRRS virus; therefore, gilts and sows were vaccinated with modified-live PRRS virus vaccine. Gilts were bred off-site and moved to the sow farm at farrowing. Several gilts went off feed at farrowing. In addition, the progeny of affected gilts showed respiratory signs and performed poorly. Nasal swabs collected from the gilts and their offspring were positive for H3N2 swine influenza virus. Some gilts died.

It was recommended that remaining gilts be vaccinated for swine influenza virus. Problems and gilt mortality continued; a gilt was submitted to the diagnostic lab. Several infectious organisms were identified. It became clear that gilts had not developed adequate immunity to the bacteria and viruses they were being exposed to in the sow herd. Nearly 10% gilt mortality occurred over a two-month period. Additional vaccination and antibiotic therapy finally reduced death loss.

An extensive gilt development plan was recommended. In addition, gilts will be moved to the sow herd once space is available.

In this situation, pathogens caused considerable mortality. Gilts were likely more susceptible because of the exposure at farrowing. Introducing gilts from high-health herds into more conventional sow herds can cause reproductive problems, although acute loss like this case usually doesn't occur.

Case Study No. 3

A breed-to-wean sow herd expanded and converted a wide grower barn to stall gestation. A center inlet from a duct built to the roof was one of the fresh air sources for the barn. The first summer the barn was in use, very high outside temperatures occurred early in the season. A fogger cooling system was not entirely functional at that time. Because the duct was not insulated and tightly sealed, and had a large surface area, incoming air actually increased the room temperature.

Late-term pregnant sows were in the center rows of the wide gestation barn, and high losses occurred due to heat stress. The ventilation system was modified to tunnel with cool cells and heat-stress mortalities stopped.


Many factors can be involved in increased sow mortality including management, nutrition, genetics, environment and disease. Often, multiple factors will be involved. It is always essential that daily individual animal observation be practiced. Being proactive can reduce sow mortality. Providing the best care possible for the sow is a welfare obligation, in addition to an economic necessity.