Poultry producers commonly face the challenge of heat stress either seasonally or year-round. Poultry farmed in hot and humid countries are genetically derived from strains originally bred in, and selected for, the cool climates of Europe and North America. Rearing birds outside of their thermal comfort zone could mean failing to achieve full genetic potential. Producers in warmer climates or those in cooler zones who adjust their shed temperatures to their own comfort levels, not to that of their birds, should consider the impact of heat stress on flocks.
Passing the upper critical bound
For any stage and any species, heat stress occurs when birds have difficulty balancing body heat production and body heat loss. Within the thermoneutral zone illustrated in Figure 1, birds are able to lose heat at a controlled rate by modifying their behavior. There is no heat stress at this point and their body temperature remains constant. At or above the upper critical temperature birds begin to pant to actively lose body heat. Panting is considered a normal response to heat, but as temperatures continue to increase, the rate of panting increases concurrently. If heat production becomes greater than maximum heat loss either in intensity (acute heat stress) or over prolonged periods (chronic heat stress), birds very quickly begin to die. The body temperature of the broiler must remain very close to 41°C. If body temperature rises above 45°C, death starts to occur rapidly.
Figure 1. The thermoneutral zone and consequences of heat stress.
Various measures can be taken to prevent heat stress. A number of options exist for nutrition and feeding strategy approaches.
- Provide adequate ventilation for number of birds housed
- Reduce stocking densities
- Insulate sheds sufficiently to avoid solar heat gain
- Position fans to optimize wind speed an air circulation
- Use evaporative cooling pads or atomizing nozzle
- Maintain water-electrolyte balance
- Vitamin supplementation
Heat stress induces unfavorable changes in indigenous bacterial microbiota. Supplementation of multi-strain probiotics may enrich the diversity of microbiota in the bird’s jejunum and caecum, restoring the microbial balance and maintaining their natural stability.
Temporary feed restriction before heat exposure can enhance thermal resistance of broilers. Feed withdrawal reduces heat production, increment speed of body temperature and mortality of broiler chickens. However, this strategy may also result in reduced growth rate, a longer growing period and a delay in slaughter age. The dual feeding program is another strategy used for broilers, which includes a protein diet during the cooler phase and an energy-rich diet during the warmer phase of each day. This maintains a nutritional balance by adequate proportion of the two diets. During a heat stress challenge, dual feeding reduces body temperature and mortality.
In laying hens, partial feed restriction or a controlled feeding regime alleviates the harmful effect of heat stress on laying performance. Changing the feeding time from twice to just once daily is also favorable to the performance of laying hens. The best time to feed the flock would be in the afternoon near sunset.
Layer diets are normally provided in mash form, but consider pellets during summer. Although feed consumption might not be affected by pelleting the ration, egg production, feed efficiency and water intake can be significantly increased in laying hens. Increased water consumption and improved digestibility of the diet is probably responsible for the advantageous effect of pelleting. Broiler chickens, however, prefer to eat more feed with larger particle size in hot environments. When corn is fed as whole grains, broilers consume more protein and have an improved feed efficiency.
Phytogenics to combat heat stress
Phytogenic feed additives (PFAs, or botanicals) are able to alleviate the negative consequences of heat stress. A recent study was conducted in Germany with a flock of Lohmann Brown Classic birds that came to lay during the early summer months at a time of high temperatures recorded in the hen houses. The birds were divided into two groups, with the control group being fed with a basal diet, while the treatment group received the same basal diet but with the inclusion of Digestarom® Poultry (a phytogenic feed additive) at an inclusion rate of 150 g per ton of feed. The trial ran from the flock age of 23 to 63 weeks.
The effects of the phytogenic feed additive during the heat stress period are displayed in Figure 2 below. The group of hens supplemented with Digestarom® in their diets consistently outperformed the control group throughout the 41 weeks in terms of hen day production, maintaining a steady peak amid the heat stress period, despite recording higher house temperatures, due to less efficient insulation and ventilation in the older building compared to that of the control group. The average hen day production of the Digestarom® group was 89.2% compared to 86.9% in the control group, representing a 2.3% increase in laying rate. There was also an improvement of feed conversion of 19 points in the birds fed diets containing the phytogenic feed additive, together with higher egg mass and average egg weights (Figure 3). The return on investment for the egg producer was 1 : 7.
Figure 2. Hen day performance and house temperatures.
Figure 3. Trial parameters and results of the heat stress study in commercial layers.
Digestarom® positively helped the flock of commercial layers to maintain their peak production throughout a period of heat stress. The birds receiving Digestarom® had better laying performance, better feed efficiency, improved feed conversion ratio, higher profitability, higher return-on-investment and better health status, with no reports of any disease outbreak. Due to its scientifically proven mode of action and unique benefits for the birds, Digestarom® successfully helped to combat heat stress, proving once again its potential as a next generation feed additive for innovative poultry nutrition and contributing to increased profits for the producer.