Can Chickens be Conditioned to Tolerate the Heat?
Jennifer Timmons, Associate Professor, University of Maryland Eastern Shore
Although the spring temperatures this year have been mild, early summer temperatures have been very warm with some days reaching near record highs. Broiler producers worked during the spring to prepare their houses and equipment so that it is working properly during the summer months. Throughout the summer, growers are always inspecting fans, cool pads, drinkers, bird distribution, generators, etc. to ensure it is all working properly when needed to keep birds comfortable. In addition to these proactive steps, what if chickens could be “conditioned” to tolerate higher temperatures? Researchers are evaluating the efficacy of early life heat conditioning to reduce the negative effects of heat stress in broiler chickens.
Birds, like mammals are warm blooded and must maintain a fairly constant internal temperature around their core or internal organs. The optimal temperature range for most market age broilers is between 65-71 degrees Fahrenheit. This is also referred to the birds’ thermoneutral zone. When birds are kept within their thermoneutral zone, they do not use energy to maintain their body temperature. Birds are heat stressed when they are not able to maintain a balance between body heat production and body heat loss. Heat stress related annual losses are estimated to be around $160 million for the U.S poultry industry.
Environmental stress such as heat stress can not only impact performance parameters for broilers, but it is also a bird welfare concern. When birds are exposed to high environmental temperatures, they display behavior responses such as less time feeding, more time drinking and panting and resting and, display extended wings.
One way to prepare chickens for high environmental temperature exposure later in life is early heat conditioning. The development of a chick’s body temperature regulation system is complete by 10 days of age. Using early heat conditioning techniques takes advantage of the chicks’ immature thermoregulation system. Studies investigating the efficacy of early life heat conditioning have been conducted pre and post hatch.
Broiler chicks complete development of their brain and body temperature regulation systems by the age of 10 days post-hatching
Pre-hatch studies have reported that increasing the temperature during certain critical periods of embryo development may stimulate the development of different physiological control systems. As a result, the ability of chickens to cope with heat stress as they reach market age might be improved. It has been suggested that intermittent heat conditioning during the development of the embryo when applied for 12 hours a day between day 7 and 16 of incubation can improve heat tolerance of broilers during acute post-hatching heat stress. In addition to thermal manipulation during incubation, other studies have exposed chicks post hatch typically between 3-5 days of age to heat conditioning temperatures. These heat conditioning temperatures were between 98-104 degrees for a 24 hour period. Similar to the pre-hatch studies, exposure to heat conditioning post hatch may induce a tolerance to high heat exposure later in life. One study reported that early heat exposure improved feed efficiency and body weight of market age broilers that were exposed to heat stress temperature later in life.
Although early heat conditioning seems like a fairly inexpensive method to help reduce the effects of heat stress for broilers, this method is not used in the broiler industry. There are multiple studies reporting the benefits of this technique however a single uniform method has not been established. Differences in breeds, market age, feed ingredients and management may result in different outcomes depending on the early heat conditioning temperature used and the age of the chick to which it is applied. Therefore, more studies are needed before this management strategy can be widely used. It also interesting to note that research investigating early age cold conditioning in broilers is also being investigated. These studies will be discussed in the next newsletter.