As in poultry, pigs are incapable of sweating in order to cool off; this makes them acutely sensitive to heat stress. Heat stress results from the combination of several factors, such as high temperatures, environmental factors (relative temperature, humidity) and an animal’s physical characteristics. Sharp rises in temperatures expose pig farms to high risks of performance drops. Therefore these periods must be handled with utmost caution.
Pigs are homeothermic animals. This feature means that they are able to maintain a stable internal body temperature of 39°C regardless of external influence. Compared with other animals, the pig is less tolerant to hot and humid conditions due to its inability to sweat. Young pigs are very sensitive to cold, whereas older pigs and mostly sows are more sensitive to heat.
Heat stress is a physiological condition when animals can no longer regulate their internal temperature. Heat stress occurs in temperate areas during summer months and in tropical areas during the whole year.
In pigs, the thermoneutral zone, or zone of thermal comfort, is simply the range of temperatures in which the pig is not cold or hot (18 to 25°C).
This condition depends on various factors:
- Humidity: Ambient temperature as well as humidity contribute to heat stress. Pigs generally develop heat stress at much lower temperatures when the humidity is high.
- Animal weight: Pigs over 75 kg weight are more sensitive to heat stress than younger pigs.
Other elements such as pen density, type of building, genetics, and air flow also have consequences on the way a pig may experience heat stress.
What are the consequences of heat stress on pigs?
When heat stress occurs, thermoregulatory mechanisms are activated. These mechanisms consist of behavioral and metabolic changes that reduce body heat load in an effort to maintain a normal pig body temperature. Common responses to heat stress in swine include decreased feed intake, increased respiration rate, and increased water consumption (loss of electrolytes) .
Several theories have been put forward to explain the negative effects of heat stress. One of the most recent theories is that damage to gut integrity plays a critical role in mediating the adverse consequences of heat stress. Animals experiencing heat stress redirect blood flow from the body core to the periphery to facilitate dissipation of body heat to the environment. The increased blood flow to the skin is counterbalanced by reduced blood flow to the gut and other body organs (liver, spleen, pancreas, and mammary glands).
In wean to finish pigs, heat stress causes decreased feed intake & increased water intake. Pigs’ average daily gain (ADG) is reduced and the feed conversion ratio (FCR) is increased. Therefore more feed is required in order to reach the same market weight (i.e. when slaughter occurs).
Decreased feed intake causes the pig to reduce its metabolic activities, thus decreasing the amount of heat produced as a result of digestion and absorption of feed nutrients.
One of these major afflictions is an increase in the permeability of the tight junctions in the gut. Increased tight junction permeability allows endotoxins commonly found in the gut to enter the bloodstream.
When pigs are exposed to heat stress their intestinal defense systems are significantly compromised ; this, in turn, provides opportunity for infection as pathogenic bacteria can invade the body more easily.
Therefore, heat stress can create secondary infection if sanitary conditions are poor resulting in the initiation of a systemic inflammatory response.
How to limit the negative effects of heat stress in pigs
Throughout the year, temperature variations resulting in high temperature peaks or sudden drops must be the object of utmost caution. These gaps can be more or less significant and depend on the geographical area (among other factors). Yet adequate precautions can be taken in order to reduce the impact of heat stress on farm profitability and animal comfort, as follows:
Feed distribution
- Divide the distribution of feed into smaller meals; supply sufficient amounts of fresh, clean water.
- Distribute the feed during cooler hours.
- Provide wet feed instead of dry feed; when using dry feed, provide it in the form of pellets instead of meal.
Nutritional value of feed
- Preferably use feed with less fiber since fiber fermentation releases heat.
- Decrease the level of indigestible protein (less metabolic heat generated) and use more synthetic amino acids according to the ideal protein concept.
- Increase the energy concentration of feed in order to compensate for decreased feed intake. Use more fat and less starch as an energy source.
- Increase the electrolytic balance with sodium bicarbonate or sodium formate.
Choice of incorporated premix
- Increase vitamins, minerals and amino acids commensurate with the high energy feed.
- Supply with antioxidants to fight ROS (Reactive oxygen species) generated by heat stress and the increase of respiratory rates : Vit E, Se, Vit C, natural polyphenols,…
- Supply with natural ingredients that stimulate feed intake, endogenous enzyme secretion and anti-inflammatory activities.
- Supply with betaine (a compound with osmolytic capacity)
There are solutions in order to reduce the impact of stress heat in pigs. The aforementioned precautionary measures can be adjusted depending on your customers' rearing conditions, on their farming context (building type, ventilation, raw materials) and the objectives sought in terms of performance. Please contact us if there is any way we can be of assistance!
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