[Skip to Content]

Illinois Livestock Trail
NOTICE - This information has been archived and may contain outdated content.
Environmental Stress
by Dr. Gilbert Hollis

Pork producers have a tendency to assume if they're comfortable inside a hog building the pigs are too. But that's not necessarily true. Pigs have specific needs and spend their time in a completely different part of the building than their caretakers.

Swine buildings need to be managed from the pigs' perspective. Here are some things to remember as you strive to provide as stress-free an environment as possible for hogs of all ages.

Pigs React to Stress

Like most animals, pigs have the ability to quickly respond to environmental stress. Although they can't always make dramatic changes in their microenvironment, pigs can modify their surroundings through bodily functions. Unfortunately, these responses to environmental stress can be counter-productive to performance. Growth and reproductive efficiency can be directly affected. Hogs under stress waste nutrients. Excessive stress can also impair a pig's disease resistance. Even if death losses don't increase, environmental stress can increase days to market and lead to uneven groups of market hogs.

According to Dr. Stanley Curtis of The Pennsylvania State University, a pig's initial reaction to stress is involuntary. The adrenal glands increase the secretion of glucocorticoids. High concentrations of these hormones help animals survive short periods of stress. However, glucocorticoids also mobilize amino acids from muscle protein and interfere with some mechanisms of the immune system.

Evaluate The Pig's Microenvironment

The environment in which pigs are expected to live and grow is really the composite of many environmental factors. These factors interact with each other. This makes it difficult to identify exactly which external condition is causing pigs to perform poorly. Therefore all environmental factors must be considered. Because some can not be easily measured, trial and error is sometimes the only way to find a solution.

It's important to obtain readings on environmental factors throughout the building. If the pigs in a particular pen always perform better or worse than their counterparts in other parts of the building, thoroughly investigate the microenvironment in those pens. You'll probably learn something that can improve the microenvironment for the entire building.

Swine managers must also keep changes brought on by the time of day or the season in mind when evaluating the environment inside a hog building. This is especially important during the season when the weather is in transition. The warm days and cool nights most parts of the country are now experiencing can cause extreme environment stress for hogs if buildings are not managed properly. Check the temperature, air movement and signs of dampness at different times of the day, especially in the spring and fall.

Rapid environmental changes cause the greatest stress. For example, if pigs are going to be moved from a temperature-controlled building to an open front finishing unit, it may be a good idea to pre-condition the pigs by dropping the temperature a few degrees a day for a week or so before moving them. Of course, this kind of pre-conditioning requires an all-in/all-out production schedule for the entire room.

How Air Quality Affects Pigs

Pigs raised in environmentally-controlled buildings have no choice but to breath the air that's present in their microenvironment. Pork producers and their employees can wear protective equipment and spend considerable time each day out of the building. Because a pig's respiratory tract is in constant contact with the air, pollutants can cause problems.

Most air pollutants found in hog buildings are created by the hogs themselves. Of major concern are microbes, dust and gases. Although some studies suggest pigs are fairly tolerant of poor quality air, these pollutants have been shown to directly alter metabolic reactions or indirectly influence the health of pigs.

The concentration of bacteria in the air inside hog buildings can be extremely high. During the summer when air must be moved more rapidly to control temperature, bacteria counts of around 500/cubic foot are common. However, these counts can swell to 10,000/cubic foot in cold weather. In modified open front buildings bacteria counts can be as high as 5,000/cubic foot, even though most fresh air only contains 10 bacteria/cubic foot.

A pig's respiratory system can normally clear bacteria from the air and keep the lungs relatively sterile. However, exposure to other environmental stresses can depress this process and leaves pigs predisposed to respiratory infections.

Dust in hog buildings is much more of a problem for workers than the pigs. Even at high concentrations, research shows dust has little direct influence on a pig's performance.

The two most important gases commonly found in hog buildings that can influence the health of the pigs are hydrogen sulfide and ammonia At acceptable levels, pigs normally tolerate hydrogen sulfide well. But this gas can be lethal to both pigs and humans above 1,000 ppm. Levels that high normally don't occur unless a pit is being agitated, but the presents of hydrogen sulfide may be a warning that a potentially dangerous situation exists.

Ammonia is present in virtually all hog buildings. Concentrations can be as high as 100 ppm. When ammonia reaches 50 ppm it can start to reduce a young pig's ability to clear bacteria from the lungs. Ammonia levels above 75 ppm have been shown to depress growth rate in otherwise healthy young pigs. There are basically two approaches to controlling air pollution inside hog buildings: Prevention and dilution. Waste management and sanitation are at the heart of any program designed to prevent harmful air pollution. A good feed distribution system is also a must when trying to improve air quality inside a hog unit.

Eliminating air pollutants is best achieved through ventilation. There is an air-exchange rate for all buildings that will virtually eliminate all infectious agents. Whether that rate is economically feasible is another question. One approach that helps dilute air pollutants without moving huge amounts of air through a building is to have high ceilings so there is more air to mix with pollutants.

Airborne bacteria and viruses generally die more quickly when temperatures are high. Sunlight can also kill microbes. Unfortunately, even in open front buildings, many microbes are protected from the ultraviolet ray in sunshine.

« Back to Swine