Heat stress and performance; a matter of balance

Heat stress in animals causes a shift in blood pH that suppresses feed intake. Of course this is bad news for the animal’s performance, so optimizing the dietary electrolyte balance (dEB) is often used as a tool to manage the blood pH. The product most often used for this is sodium bicarbonate. We believe that sodium formate is equally effective at managing the dEB of feed. Last August we put this theory to the test.

Dietary electrolyte balance and animal performance
To help animals cope with heat stress several solutions have been offered and dietary addition of sodium bicarbonate is a successful tool to manage dEB. Many researchers have shown that diets with a correctly calculated dEB have the potential to improve bird survival during heat stress. Borges et al (2003) showed that a practical dEB ranges from 220-240 mEq/kg in broilers raised in summer conditions.

Sodium formate and dEB
Last August the use of sodium formate was evaluated in broilers raised under summer conditions (IMASDE, Spain). The object of the trial was to investigate whether the efficacy of sodium formate was equivalent to that of sodium bicarbonate in broilers (Ross 308) raised to market weight at 42 days of age under summer conditions. Temperature inside the building was set at 33-35°C. The dEB was 240mEq/kg in the starter phase and 244 and 250 in the finisher phase for sodium bicarbonate and sodium formate respectively.

It was shown that at day 42 there was little difference between the two treatment groups for the production parameters; daily gain, feed intake and FCR. Sodium formate gave a better FCR up to 21 days of age. Furthermore, sodium formate showed the lowest mortality (4,9% versus 7,2%). In general both groups performed remarkably well given the set conditions. It can be concluded that sodium formate is a very good alternative for sodium bicarbonate to optimize the dEB and thus help animals to perform while under heat stress. ProPhorceTM AC 299 is Perstorp's brand of sodium formate with excellent free flowing characteristics.

What is heat stress?
Poultry are warm-blooded animals which are capable of maintaining their body temperature at a relative steady level despite varying environmental conditions. Body heat is a balance between heat production and heat loss. The metabolism of proteins, fats and carbohydrates produces heat whereas conduction, convection, radiation and evaporation cause heat loss. The animal will start to use thermoregulatory adaptations such as panting to lose heat. When heat production is greater than heat loss a situation called hyperthermia occurs. At this point heat stress will become an issue. It is a problem for animal welfare and results in reduced productivity.

Today the modern broiler with high growth rates and high stocking density is more prone to problems with heat stress especially in high ambient temperatures. To help the animal cope with heat stress several adjustments in general bird management can be made. Adjustments such as:

  • - continuous fresh air by means of air flow
  • - decreased stocking density
  • - adjusted feeding schedules
In extreme situations animals start to drink more water which leads to wet litter and an increased loss of electrolytes. Also the animal starts panting to lose heat by means of increased evaporation. This results in respiratory alkalosis and therefore a change in the acid-base balance of the blood. A shift in blood pH suppresses feed intake and therefore affects performance in a negative way. A solution is to manage the acid-base balance in the blood via the dietary electrolyte balance. The tests mentioned earlier have shown that Sodium formate is as good a tool as any to manage dEB.
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Gonny van Helvoirt
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