Barn temperature, temperature fluctu-ation, humidity levels, drafts and gases all have documented roles on their ability to affect swine health, says Michael Eisenmenger, DVM, a swine veterinarian with Swine Vet Center, St. Peter, Minn.

“As veterinarians in the field looking at pigs and their environment on a daily basis, the large impact these parameters have on pig health becomes extremely clear to us,” Eisenmenger pointed out in a presentation during a seminar at this year’s American Association of Swine Veterinarians Annual Meeting in Toronto. The seminar was titled:  “Applied swine medicine: Taking it to the farm.”

Eisenmenger says that environment has the ability to affect, among other things, how pathogens spread through a barn, survival times of pathogens in the pig environment, exposure levels of pathogens in the barn and concurrent stress levels in the animals.


Environmental factors, such as building temperature, temperature fluctuation, humidity levels, drafts, and gases all have documented roles on their ability to affect swine health.

As a result, environmental factors can “strongly influence disease levels within barns,” he says.

Eisenmenger looks at the following specific environmental factors that can impact swine disease in a production system:

Humidity can be an excellent gauge for minimum ventilation rates in cool months when the barn is attempting to run minimum ventilation. “Most of the time, if we are meeting humidity standards, we will also be achieving correct gas levels within the barn,” says Eisenmenger. “If humidity levels are correct and gas levels are abnormally high, then we need to be exploring reasons, such as pit problems, for excess gas production.”

Measurement of relative humidity within a barn can be done with an inexpensive thermohydrometer, but the more expensive thermohydrometers are more accurate, last longer and can be read quicker, according to Eisenmenger.

On the other hand, relative humidity probes that hang in the barn and are operated through the controllers historically have tended to be inaccurate and short-lived in commercial settings.

Goals for humidity levels in swine confinement buildings should be 50 percent to 70 percent, says Eisenmenger. “Relative humidity should only be measured when minimum ventilation is running in the room. Once you are above minimum ventilation rate and begin to ventilate on the heat removal curve, it becomes a worthless measurement. Low humidity – below 50 percent –  in the wintertime can be achieved by burning excess LP and over-ventilating the room. High humidity – more than 70 percent levels – is induced by under-ventilating the room and allowing the moisture produced
by the pigs to reach high levels.”

Eisenmenger says you should always measure relative humidity objectively with a thermohydrometer. “Don’t trust how the room ‘feels.’ Barn personnel tend to be inaccurate at estimating humidity levels and often when working in a warm to hot environment, they will complain that it is also humid when the range is in normal parameters.”

The ambient temperature of the barn is dependent on many factors, says Eisenmenger. In a typical full-slat, double-curtain or tunnel-ventilated barn, for example, temperature curves would normally range from 88°F to 62°F from wean to finish.

“In the wean‑to‑finish or nursery stage, the 88°F can be in very specific zones in the barn, and the entire barn does not need to be this temperature. In addition to ambient barn temperature, the rate of fluctuation within a pig barn is also extremely important.

“Cool temperatures, as well as draft conditions, can cause very high levels of stress in pigs. This is classically exhibited with cold-stressed wean‑to‑ finish pigs that get diarrhea shortly after placement.

“Heat-stressed pigs in the summer leading to clinical cases of ileitis, along with depressed feed intakes and subsequent gastric ulcers, is also an example of temperature stress.”


Improperly operating fans can strongly influence disease levels within pork production buildings.

Hanging a high/low thermometer in the room is a good method for measuring temperature because you can go to specific areas within the barn and measure the high and low range of temperature at that location, says Eisenmenger. “It is important to realize that mercury thermometers respond slowly, and they will not pick up rapid changes of temperature fluctuation.”

A room temperature probe also is important because this is the device that is driving the ventilation controller to run heaters, fans and curtains. “Probe placement is extremely critical,” says Eisenmenger. “You do not want the probe in either an under‑responsive or over‑responsive area of the barn because it could drive the controller to do abnormal things.

“An example of an under‑responsive probe location leading to wide temperature fluctuation in the barn would be a probe that is insulated from the actual ambient environment in the barn, such as in a PVC tube.

“An example of an over‑responsive probe would be a probe that is placed in front of inlets or heaters.”

It is also important to realize that most probes tend to respond slowly and therefore will not pick up rapid temperature fluctuations within the barn similar to a mercury thermometer, according to Eisenmenger.

Temperature recording device
Eisenmenger says for years he has used a SAPAC (Monitor Company) controller with an external stainless steel probe to record temperatures.

“The monitor has an external start and stop button so you can program it before getting to the barn and turn it on just before entering the barn. It can be completely submersed or wiped off with a disinfectant to allow for biosecurity between pig buildings.

“It has been an excellent tool to help set and fine-tune ventilation within the commercial nursery and finishing systems. It is also an excellent visual tool to help producers understand how the ventilation controller can actually affect temperature fluctuations in the barn.

“Many producers have firm beliefs of how ventilation should be set, and we, as veterinary consultants, are not going to change their beliefs just by telling them they are wrong. We must show them. There are many other automated recording devices on the market. Check durability, and response time before purchasing.”

Managing temperature

Eisenmenger offers the following tips for managing temperature fluctuations:

  • Curtain settings. Because different controllers manage curtains in many various ways, it is critical that you develop a thorough understanding of the capabilities and limitations of each controller system, says Eisenmenger. “Some advanced controllers will allow the first move of the curtain to be different from the rest and can move the curtain up faster than it goes down. Other controllers are limited by simply an on-time and an off-time for both the up and down movement. Use the recorder in the barn and experiment with multiple settings to see what is the best combination. The key is to let the barn react to the new temperature before calling for another move.”
  • Keeping curtains up as long as possible. “This is the most important step. Clearly, the more cfm capacity per pig in the barn, the higher the outside temperature can be before the curtain needs to make a move. “Often, I see barns in which total cfm capacity is not allowed to be used due to fans being plugged or not operational, dirty fans, inlets within the room not allowed to open, or eave inlets plugged and not allowing air into the attic.”  Eisenmenger recommends that you check to ensure that all fans are operational, all fans/shutters are clean, inlets are set so they can open, there are enough inlets to match cfm total of barn (total cfm/800 ft/min = sq. ft inlet needed) and enough soffit inlet space (total barn cfm/500 = sq ft needed).
  • Bandwidth on stage 1 and stage 2 fans set too tight.A bandwidth on a particular stage on a controller is dependent on the number of cfms per pig within that stage. In general, says Eisenmenger,  the greater the cfm per pig on an individual stage, the wider the bandwidth should be. “Rarely, if ever, should bandwidth be set less than 1. Experiment with a SAPAC or similar device. Set bandwidth to higher and lower values and measure how the barn responds.”
  • Incorrect probe placement. “It was not unusual with some of the barns built in the late 90s and some remodel jobs to have the probe inside a PVC tube hung near the floor,” says Eisenmenger. “This insulates the probe from the ‘real’ temperature of the room and therefore allows wide temperature fluctuations within the barn. Often, the probes are placed in a barn as an afterthought based on cable lengths and are directly in front of inlets or a heater. A probe that is in front of a heater will think the room is too warm and cause fans to ramp, leading to increased LP usage. A probe that is in front of an inlet will think the room is too cool, causing the heater to run.”


Eisenmenger explains that incorrect inlet settings can cause a barn to fluctuate in two ways. “Not having enough inlets to meet the total fan capacity of the barn will cause the curtains to come down sooner, potentially leading to larger temperature fluctuations in the barn.

“Attic inlets (soffit inlets) that are plugged (made of the wrong material: residential material versus bird screen) will cause the negative pressure within the room to get too high, causing curtains to be sucked tight against the barn.

“Even though the controller is telling the curtains to go down, negative pressure within the barn is holding them up. Then when they finally do make a move, it is one big move, which is too large and leads to too much cool air coming into the barn.”  

Some common humidity and temperature mistakes

Minnesota swine veterinarian Michael Eisenmenger points to these common mistakes that can be found when troubleshooting humidity and temperature fluctuation problems:


  • Over-ventilation for worker comfort.
  • Under-ventilation due to: minimum setting incorrect; controller does not match fan output; wind, especially big fan running at low speed; and too high negative barn pressure (not enough inlets, inlet set closed, attic under-ventilated, soffit inlets plugged).

Temperature fluctuation

  • Curtains go down too soon, not allowing enough air in barn. This can be caused by not enough fans, dirty or not working fans, plugged soffit inlet, not enough room inlets and inlets set to incorrect position.
  • Incorrect curtain settings.
  • Bandwidth set too narrow.
  • Probes protected from actual barn temperature.
  • Probe near inlets or heater.
  • Heaters too large or heater off sets and differentials not set correctly.