By Jonathan Holt, North Carolina State University Department of Animal Science
Heat stress results when the pig is unable to dissipate heat energy produced from digestion and metabolism into the environment to lower its core temperature to a comfortable range. Problems with heat stress are also on the rise with the recent trend for improved genotypes of swine that grow faster and leaner, but at the same time produce more body heat due to the increased metabolic activity.
Growing and finishing pigs have an ideal air temperature of 60-70 degrees Fahrenheit and experience heat stress if exposed to air temperatures of 80 degrees F or higher for more than one hour in a 24-hour period. In response to heat stress, growing and finishing pigs will decrease their feed intake in an effort to reduce the amount of body heat they produce.
This loss in feed intake will reduce growth rate and often result in inconsistent market weights during periods of heat stress. Research by Rauw et al. (2015) has also shown that heat stress can negatively influence carcass characteristics of pigs exposed to repeated heat stress. Behavioral changes also occur when growing and finishing pigs are exposed to environmental heat stress. Not only does water consumption increase, but the pattern in which pigs drink water throughout the day changes. These changes often persist for days even if the heat stress has been alleviated. Further information on the effects of increased water intake on nutrient requirements as well as using drinking behaviors to predict production problems is needed. All of these factors contribute to massive economic losses to the US swine industry associated with heat stress.
As summer is now upon us, it is important to remember some of the following tips to be prepared for potential heat stress in your growing and finishing pigs.
Adjust summer diets
Since pigs will decrease feed intake when temperatures increase, it is important to increase the nutrient density of the diet. One common method is to add supplemental fat to the diets in order to increase the caloric intake of the pigs. However, remember to increase the density of all nutrients (including vitamins and minerals) or performance may still suffer. Another potential feeding strategy during hot weather is to lower the crude protein of the diet by adding synthetic amino acids. Lowering crude protein levels will help the pig lower the amount of heat produced during digestion.
Ensure proper water supply
Drinkers should be cleaned and functioning properly to provide unlimited access to fresh water. Growing and finishing pigs will consume 3-5 gallons of water per head per day. However, during heat stress, this may increase by up to six times. If flow rates of the nipple drinkers have not been checked recently, now is the perfect time to do so. Flow rate from nipple drinkers should be between 0.5 and 0.67 gallons per minute for growing and finishing pigs. Also, to ensure enough water is provided to each pig, you should have no more than 12-15 pig per nipple drinkers in a pen. One aspect that may be overlooked during heat stress is potential problems associated with electrolyte balance of the pig. Increased water intake leads to increased urine output, which could increase mineral excretion as well. This area of nutrition for growing and finishing pigs is not well understood.
Check and maintain ventilation and cooling systems
It is important that all equipment related to cooling is functioning properly. Check thermostats for correct settings as well checking air inlets and fans for cleanliness. Also test and check sprinklers or drip systems to make sure water is flowing correctly. Large water droplets are better than a fine mist, since a mist may raise humidity in the barn. Remember, temperature and humidity contribute to the heat that animals will feel in the barn and controlling both is an important aspect of cooling. Increased humidity may require alterations to ventilation fans in order to maintain temperature. Air movement over the pig can help with evaporative cooling, therefore, ventilation should be adjusted during hot weather. While ventilation rates for growing and finishing pigs during mild temperatures should be around 24-25 cubic feet per minute/pig during mild temperatures, this rate increases to 75-120 cfm/pig during hot weather.
Recent work at North Carolina State University was conducted to determine effects of an induced heat stress on growth performance and eating and drinking behaviors of growing pigs. Pigs (n=32; average BW approximately 93 pounds) were housed individually in thermo-neutral conditions or subjected to constant high ambient temperatures (mean 82 degrees F) for 15 days, followed by a seven-day recovery period at 68 degrees F. Frequency and duration of eating and drinking were recorded. Pigs subjected to heat stress had had lower average daily feed intake and average daily gain compared to pigs housed in a thermoneutral environment during the first week. Unexpectedly, pigs subjected to heat stress still had lower feed intake during the recovery period compared to pigs housed in a thermoneutral environment. This trial had a longer, constant heat stress, whereas other similar trials have short-term heat stress which may have contributed to the lack of recovery of feed intake once the temperatures were lowered. Pigs subjected to heat stress also ate less frequently in the morning compared to pigs kept at thermoneutral temperatures.
Regardless of treatment, pigs drank more frequently in the evening compared to the morning. We are continuing to study the effects of a longer-term heat stress on growing and finishing pigs while also determining the impact of this stress on inflammatory cytokine responses. The more we learn about the multi-factorial impacts of heat stress on growing and finishing pigs, the more equipped we will be to reduce the negative side effects.