June 21, 2012 - Elevated temperature above 30°C combined with elevated humidity results in reduced feed intake and possibly heat prostration mortality in poultry. As well, flock performance and health may be compromised with reduced intake of vitamins and minerals.
Research shows that thiamin requirements double during heat stress, and there is also a reduction in the absorption of fat-soluble vitamins ADE. This is concurrent with an increasing excretion of minerals such as sodium Na+ and potassium K+, which negatively affects the heat dissipation capacity and acid base balance resulting in losses in growth performance.
There are five modes by which birds get rid of excess body heat:
- Conduction - Contact of a warm surface with cooler one will allow heat transfer. Hot birds will try to cool down by touching water pipes or digging into litter to contact a cool floor. In extreme cases, the breast muscle will develop a pale, cooked appearance after the bird sits for prolonged period time.
- Convection - Moving air over the birds is the most effective way to keep them cool. If air is not moving quickly enough, heat will build up around their bodies. In extreme heat situations, birds are often found dead along walls where air does not circulate efficiently. These birds usually die from heat prostration, and not from lack of oxygen.
- Radiation - Birds will raise their wings to allow heat to radiate from areas where feather cover is poor. Note that many leghorns survive well in cages because of poor feathering and lack of floor litter, which permits maximum radiation.
- Excretion - Birds will typically double their intake of water during periods of heat stress and thus excrete more hot urine and water in feces. It is therefore especially important to ensure your barns have an appropriate drinker ratio, clean water filters and well-adjusted pressure regulators to maximize water delivery during warm weather.
- Evaporation of water - This occurs from the surface of the skin and from the respiratory tract. In heat stress conditions, the bird will try to maximize heat loss by panting. Respiration rates may increase as much as tenfold, resulting in excess carbon dioxide (CO2) loss. In extreme cases, this loss can change blood chemistry leading to death.
Under heat stress conditions, maintaining water and electrolyte balances are important factors affecting survivability and productivity, especially with high humidity. An essential component to cooling is by high velocity air movement over the birds, but when they are housed under high density, it is absolutely necessary to encourage access to water preferably medicated with vitamins and electrolytes.
Respiratory rates may also increases tenfold with excessive losses of CO2. The acid base balance is disrupted with birds altering metabolism towards homeostatic regulation rather than processes supporting growth.
Excessive water is lost through panting and higher urine flow, which negatively influences the capacity to dissipate heat. Unfortunately there is excessive loss of sodium and potassium in to the urine and feces. The sodium, potassium and chloride ions are important in maintaining the acid-base balance and cell membrane integrity.
Electrolyte supplements can enhance water utilization by increasing water retention, and researchers have reported that sodium chloride and potassium chloride, when administered in the water, were able to alleviate the adverse effect of heat stress.
Gut lining integrity is also compromised under heat stress conditions thus interfering with the absorption of essential vitamins and minerals.
In summary, the valuable vitamins and electrolytes loss with rapid respiration and increase urine output must be replaced or the bird suffers decreased weight gain or even death. In many cases the few dollars spent on water medication will have a significant effect upon the productivity of poultry and livestock.