As summer temperatures continue to rise, one of the biggest issues facing laying hen producers is heat stress. Heat stress causes many physiological issues that lead to economic losses, including increased oxidative stress, improper acid-base balance, and suppressed immune systems. Though there are many environmental strategies to cope with the troubles of heat stress, feeding buffers, such as sodium bicarbonate, can help restore the acid-base balance and aid in sustaining egg production and shell quality.

Importance of the Acid-Base Balance

Birds do not have sweat glands and cool themselves through evaporative cooling, or panting. During panting, birds excrete more carbon dioxide (CO2) than cells can produce, causing a change in the normal buffering system in blood. The reduced CO2 in the body decreases the amount of hydrogen ions and carbonic acid, leading to a higher blood pH. To get blood pH back to normal, birds will begin to retain more hydrogen ions and release higher amounts of bicarbonate ions from the kidney, which can lead to metabolic acidosis and respiratory alkalosis, both of which are associated with a decrease in performance (Borges et al., 2007). If birds are unable to restore their acid-base balance back to normal, feed intake lowers, production drops, and increases in mortality could occur.

Dietary Equilibrium Balance

The dietary equilibrium balance (DEB) is crucial in helping to maintain the proper acid-base balance during heat stress. DEB is calculated by the formula of Na/0.023 + K/0.039 – Cl/0.035. Electrolytes (sodium, potassium, and chloride) are crucial compounds that can dissolve into positively and negatively charged particles to help restore proper blood pH. During heat stress, a higher DEB of 250-300 mEq/kg has been shown to mitigate the negative effects of the acid-base imbalance (Mushtaq et al., 2013) and restore normal growth and production parameters. One of the cheapest and most effective ways to create this higher balance is through increasing levels of sodium bicarbonate, which is often referred to as the electrolyte of choice as it contains both sodium (positively charged) and bicarbonate (negatively charged) ions, and it is readily available in the market, and economical feasible to poultry producers.

Shell Quality Benefits Associated with Sodium Bicarbonate

One of the biggest issues associated with heat stress in laying hens is shell quality. The reduced bicarbonate levels in the blood during heat stress is detrimental to the formation of the eggshell as bicarbonate is needed to buffer hydrogen ions that are produced during shell formation (Frank and Burger, 1965). Multiple studies have shown that eggshell quality issues caused by heat stress can be ameliorated with the incorporation of sodium bicarbonate (Makled and Charles, 1987; Balnave and Muheereza, 1997). In fact, Makled and Charles determined that access to sodium bicarbonate during eggshell formation is crucial to increasing shell integrity. Additionally, sodium bicarbonate can neutralize excess gastric acid produced by the proventriculus, increase feed intake, and improve digestibility of nutrients.

In conclusion, sodium bicarbonate is an effective way to mitigate the negative effects of heat stress in laying hens. The optimum buffering capacity of sodium bicarbonate restores the acid-base balance to a normal level, increases the levels of bicarbonate in the blood, and can aid in restoring and maintaining shell quality during hot and humid temperatures.