Effect of Summer Heat Stress on Poultry Breeding Stock

As the hot summer months approach producers’ attention is turned to management methods designed to maintain productivity during elevated ambient temperatures. For broiler and turkey meat producers, getting the birds to continue eating and efficiently converting their feed source to weight gain is the overall objective. The effects of heat stress have been well documented in relation to feed consumption, weight gain and house efficiency in broilers. In extreme heat situations, keeping birds alive becomes the most critical element, especially in older meat-type birds.

For producers of broiler breeders, the volume of feed the birds consume is restricted, so even during elevated temperatures the birds will often still consume the feed provided to them. This is especially true for broiler breeder males that will generally eat all the feed provided them in less than an hour during both summer and winter months. During this time of the year, however, the birds’ energy needs are reduced, and therefore, they do not require as much feed for maintenance as they do during the winter months. The problem with breeders is maintaining egg production, fertility, hatchability and ultimately the number of quality chicks produced. We, as an industry, have come a long way in the utilization of quality equipment in the breeder houses and therefore in reducing in house temperature spikes. Twenty years ago it was estimated that there was an average 15% drop in fertility in broiler breeders during the summer months. Due to improvements in housing, the reductions in fertility due to heat stress may not be so dramatic today. Nevertheless, the industry generally sees the lowest fertility and hatchability during the hot summer months.

Why does this occur?

There is undoubtedly a connection with elevated temperatures and reduced mating frequency, which naturally reduces fertility. However, there is also evidence that elevated temperatures reduce sperm production and overall semen quality. To determine the role that the male and female broiler breeder plays in the reduction in hatchability during heat stress conditions, a study was conducted to measure various reproductive parameters. Broiler breeders males and females were separately exposed to one of three temperatures (70º F, 85º F, or 90º F) during an eight-week test period and artificially inseminated weekly. Although various semen characteristics were not affected by heat stress in this study, the ability of the sperm cells from heat-stressed males to gain access to the site of fertilization was reduced in heat-stressed groups. Additionally, the duration of the ability of sperm cells to fertilize eggs was also reduced in both the 85º F and 90º F heat stressed groups of males. However, the effect of heat stress on fertility was less significant when only the hens were exposed to the elevated temperatures. When comparing hatchability of fertile eggs from both heat-stressed males and females, there was reduced actual hatchability, although this was not significantly different.

In summarizing this work, it is apparent that elevated temperatures affect the males ability to produce fertilized eggs using artificial insemination as a means to produce fertile eggs. This means that the physiology of the male reproductive system is hindered and the production of viable semen is reduced. Interestingly, when these males were subjected to 85º F or 90º F for as little as 12 hours, fertility was reduced for the next four to five weeks. Breeder house temperatures in the 85 to 90 degree range for periods of time during the summer are common in many breeder houses, especially those that have not been updated with modern evaporative cooling systems. Therefore, it is easy to see why hatchability is often at its lowest during the summer months.

Preventing heat stress in breeders

Here are a few of many items that should be considered that may help reduce the incidence of heat stressing breeders.

■ Air velocity is most important in keeping birds cool in the summer. Any adjustments made to thermostat settings should be made with the idea of maintaining temperature while not sacrificing wind speed.

■ Turn fan thermostats down low enough during the daytime hours to ensure that they will run long enough into the evening to give birds a chance to cool off. During extreme heat, run all fans throughout the night to allow birds to cool off completely.

■ Run a lower static pressure during hot weather to get the maximum volume of air movement from exhaust fans.

■ Remove shutters from any fan that runs continuously. This will increase airflow through the fan by as much as 30 percent.

■ Make sure fan belts are tight and new. A loose belt can reduce fan efficiency by 30 percent or more. Even tight belts that are worn and old pulleys can reduce fan efficiency by 20 percent.

■ Make sure roof or sidewall ventilation openings are clean and unobstructed.

■ Inspect emergency generators, automatic curtain (or sidewall) drops and alarm systems to ensure they are functioning properly. Failure of this equipment to function properly will most likely result in catastrophic losses.

■ Water is critical during hot weather. Inspect the watering system frequently to ensure water flow is consistent and unrestricted.

■ Water in a closed watering system will quickly approach the temperature of the air around the pipe. Water consumption will decrease when the temperature of the water rises above 85 degrees. Flush the closed watering system two to three times each day during the hottest part of the day to remove warm water from the system. However, the birds will generally demand enough water to keep fresh water in the pipes.

References

McDaniel, C.D., R.K. Bramwell, J.L. Wilson, and B. Howarth Jr., 1995. Fertility of Male and Female Broiler Breeders Following Exposure to Elevated Ambient Temperatures, Poultry Sci. 74:1029-1038.

By R. Keith Bramwell, Extension Poultry Specialist
Cooperative Extension Service, Center of Excellence for Poultry Science
University of Arkansas
AVIAN Advice • Summer 2003 • Vol. 5, No. 2