The Cost of Heat Stress in Pig Herds

Heat stress in pig herds is a challenge faced may places in the world. The challenge depends on multiple factors, including the climate and the house type/design.
This article will focus on heat stress among pigs in a Danish context, but many of the challenges discussed and solutions suggested can be applied elsewhere in the world too.

The ventilation system in a pig house that was built in the 1980s was designed to accommodate sows that weighed 200-250 kilograms. However, with the current weight of sows reaching up to 300 kilograms, it is necessary to adjust the system accordingly.

Heat stress is a common problem among sows; in the worst case, it can lead to death. Reduced feed intake is also a result of heat stress, which can cause sows to lose weight and produce less milk. This has a negative impact on reproduction and subsequent litter.

In addition, there is a welfare concern, as animals not receiving proper cooling is a significant problem in itself. Therefore, examining your ventilation system is crucial if you are dealing with heat stress.

There is also an economic aspect to consider. Depending on the economy, it costs approximately 1,000 euros when a sow dies in late gestation. This includes the sow’s slaughter value and the production value of the piglets that the sow was either pregnant with or would have cared for in the farrowing pen. The death of a sow affects the contribution margin in the farrowing pen, piglet pen, and slaughterhouse of a full-line herd.

According to an analysis conducted by SEGES Innovation, a Danish independent research and development organization within agriculture, the number of sows dying increases in the summer months from June to September. Based on the report, our calculations show an increase in mortality among Danish pigs of 0.8 percent during the summer months. Therefore, it is important to examine and adjust the ventilation system to prevent heat stress and ensure the welfare and productivity of the animals.

Difference in sows 1990-2024

Highly productive sows

Danish pig houses are equipped with ventilation systems. So why do we still observe heat stress and increased mortality?

When we visit older houses, we often find that the ventilation capacity is not sufficient anymore. The basis for many heat production calculations dates back to 1984 when a sow averaged 200-250 kilograms and had ten live-born piglets per litter. Today, sows easily have 18 live-born piglets, and their weight has increased to nearly 300 kilograms. Additionally, the house’s usage may have changed from continuously introducing and removing sows to relatively large groups being introduced and removed from individual house sections.

The sow's heat production increases up to 40 percent during gestation. If group housing is practiced with relatively large groups, heavily pregnant sows may suffer from excessive heat on one end of the house, while recently mated sows on the other end may produce much less heat and be more comfortable as air is distributed evenly throughout the house.

Example from Denmark

Consider an example from Denmark, where a gestation house with 400 sows may experience a temperature above 25 degrees Celsius for around 460 hours each year.

Typically, such houses have a ventilation capacity of 50,000 cubic meters per hour, which translates to 125 cubic meters per sow. At maximum ventilation capacity (100 percent), which is 125 cubic meters per hour per sow, the chill effect of the air feel will make the pigs feel 1.5 degrees Celsius cooler than the actual temperature. Taking the chill effect into consideration ensures that there are now only 240 hours out of the 460 hours where the temperature is perceived as over 25 degrees Celsius.

What can you do?

Fortunately, there are ways to ensure that your ventilation system functions properly.
It's important to measure whether it performs as it should and keep the air intakes and exhaust units clean from dust and such.

If you have old triac-controlled fans installed, ensure that the capacitors are not worn out as it causes the fans to perform below their original capacity.
During the summer period, with the clear sky, the attic space of a house can get very hot. In such cases, using a sub-roof or insulating the roof surface is recommended when drawing air from the attic. Installing solar panels on the roof to absorb the heat can also be beneficial.

In houses with sloped ceilings, be aware of skylights as they provide good light but also generate plenty of heat, like in a greenhouse. When we dimension for the warmest summer days, we estimate that a house with skylights will add up to 500 W/m², which requires additional chimneys and fan capacity to eliminate. Alternatively, large fans can be placed in the gable.

Factors to consider for the best climate for pigs

Ensure sufficient ventilation capacity

  • Pregnant sows in continuous operation require 125 cubic meters per hour.
  • Pregnant sows in group housing require 145 cubic meters per hour.
  • Lactating sows require 375 cubic meters per hour.

Account for attic space and skylights

  • Reduce solar heating when drawing air from the attic – consider using a sub-roof or installing solar panels on the roof.

Implement cooling methods

  • High-pressure cooling.
  • Pad cooling.
  • Overhead misting.

Increase air velocity to achieve a chilling effect

  • Direct air onto the animals during high outdoor temperatures.
  • Install air circulators/fans suspended in the house.

Additionally, you should consider when to feed. Preliminary studies from SEGES Innovation indicate that heat production increases by up to 75 percent immediately after feeding.
Therefore, one might consider feeding early in the morning to avoid adding more heat during the warmest hours. Typically, the warmest period is from 2 PM to 6 PM.

Regardless, if the sows are panting or if there is higher mortality than usual, action should be taken. Do not accept sows that are too hot. If you have any doubts, you can always contact your local SKOV sales manager or speak with a service technician – they are trained for such situations.