Physiological Responses of Poultry to the Environment - Poultry [Skip to Content]

Illinois Livestock Trail
Physiological Responses of Poultry to the Environment
by Ken W. Koelkebeck


The "environment" can be defined as the combination of external conditions (biological and physiological) which affect or have an impact on animals and humans. The external conditions such as weather and climate can affect animal production and physiological responses, however, with poultry the environment usually are those external conditions which are found in the birds microenvironment. These are factors such as nutrition, water, air, temperature, humidity, light, disease, social, sound and wastes. Poultry producers try to control these factors, so that the bird can maintain normal physiological functions and produce meat or eggs at its maximum rate. The overall effects of the birds macro- and microenvironment is depicted in Figure 1.

When considering the birds microenvironment, management is the key. If the birds light environment is managed in the proper way, then egg production for layers and growth for broilers and turkeys can be maximized. However, if improper light stimulation is practiced, then egg production and growth will be inhibited. Another factor of the birds microenvironment which needs to be managed properly is temperature. If the poultry house environmental temperature is allowed to exceed normal ranges, then egg production, egg size, and growth will be negatively affected. These factors along with others affect the birds metabolism which in turn is responsible for the output of eggs, meat, and body heat to maintain normal physiological processes and functions. Figure 2 depicts the effect either positive or negative of environmental factors on energy metabolism and the production of eggs, meat, and heat.

For poultry, the maximum production of eggs or meat requires that energy gained by the bird from the feed is utilized in the most efficient manner as possible. Along with the utilization of energy by the bird, other things such as protein, vitamins, and minerals must also be used efficiently in order to produce the most eggs or gain the most weight. If the factors that affect the birds physiological performance are not kept within proper limits, then the environment is considered to be a stressor. It has also been shown that these environmental stressors such as hot temperatures, high air humidity, etc., may affect the bird in an additive manner if these stressors are imposed concurrently. These stressors can negatively affect chick growth performance, feed intake and efficiency, and physiological status.

Physiological Responses of Poultry to Social Stressors

One of the often overlooked stressors that affects production efficiency and physiological responses of poultry is social stress caused by overcrowding. This can occur in layers housed in multiple-bird cages and in broilers housed in intensively confined floor pens. It has been documented that productivity rate generally declines as population size increases and space allowance per bird decreases. The birds main physiological response to the social stress interactions of many birds housed in a cage is an increase in the circulating levels of corticosterone (adrenal gland hormone) found in the blood. A typical physiological response is the for the birds to react to social stress by releasing corticosterone from the adrenal glands as a protective mechanism. Early work by Koelkebeck and Cain (1984) showed that blood levels of corticosterone of layers kept in multiple-bird cages and floor pens were elevated in response to increased social stress. These studies also showed that decreased productivity occurred for layers exposed to these social stressors. Figure 3 shows that corticosterone levels of laying hens sampled from floor pens were elevated for those maintained at a density of .094 m2/bird versus those maintained at .373 m2/bird (Koelkebeck and Cain, 1984). In addition, egg production, percent livability, and average body weight were depressed for those birds maintained in floor pens versus those kept in cages (Table 1).

Thus, the previous work suggests that the number of hens kept per cage and the type of rearing environment (cages versus floor pens) does affect the birds productivity and physiological response to these social stressors. Therefore, it is important in commercial operations that producers not overcrowd pens or cages.

Physiological Responses of Poultry to Light

One of the most common physiological effect of light on growing poultry is the effect of daylength on how early or how late birds become sexually mature. If leghorn pullets and broiler breeder pullets are grown under an increasing daylength, then sexual maturity will be enhanced which can cause egg production and blowout problems in the layer house. If pullets are grown under a decreasing daylength, then sexual maturity will be delayed. In most practical poultry production situations, pullets are usually grown under photoperiod lengths which are decreasing or constant. In addition to the physiological effects of photoperiod length, light intensity can also affect poultry. If pullets, layers, and growing birds or turkeys are grown and maintained in non-light controlled facilities, high light intensity may cause feather picking and other related problems.

Since physiological and production responses of poultry can be greatly affected by light and lighting programs, it is advantageous that producers use light-controlled facilities if possible. For example, the following beneficial results would occur if broiler breeders were to be raised in light-controlled facilities.

  1. Greater control of age at sexual maturity
  2. Consumption of growing and laying feeds are reduced with an economic savings.
  3. Flock uniformity is better

Controlled-lighting facilities are also advantageous for rearing leghorn pullets. Some of the advantages for using controlled-lighting facilities are:

  1. Subjecting pullets to short daylengths during the growing period increases the number of eggs laid during the first half of the egg production period.
  2. Reductions in the length of light during the growing period lengthens the time from day 1 to sexual maturity.

Physiological Responses of Poultry to Heat Stress and Multiple Concurrent Stressors

Perhaps the most important physiological response of poultry to the environment is the constant maintenance of a homeothermic state (constant body temperature) during exposure to extreme ambient temperatures. Poultry respond physiologically to cold temperatures by mainly by increasing internal metabolic rate to keep their body temperature normal. During exposure to hot ambient temperatures, poultry have a more difficult problem keeping themselves cool and maintaining homeothermic body temperature. Since birds do not sweat, they must rely on evaporative cooling (panting) to keep themselves cool. This increased rate of panting produces what is called respiratory alkalosis of the blood. This physiological response is characterized by an increase in blood pH (more basic), along with a decrease in blood CO2 concentration. This upsets the blood acid-base balance and produces a decrease in blood calcium and bicarbonate which are necessary for the production of strong egg shells. Thus, the ultimate problem is a production of thin-shelled eggs produced by laying hens. As for growing birds, heat stress affects them by depressing weight gain mainly because feed intake is depressed. Figure 4 depicts the response of poultry to extremes in environmental temperatures.

In our laboratory, we have conducted several studies in which we have developed a system that is designed to replenish the CO2 lost in the blood of poultry (laying hens) when they are exposed to high temperatures and are panting. This system (Figure 5) provides the bird with a constant source of carbonated drinking water. Previous results in our laboratory have shown that egg shell quality could be improved for layers exposed to high environmental temperatures (Odom et al., 1985). In more recent work, we showed that egg specific gravity of second-cycle hens maintained in a commercial-type facility during the summer was improved by providing carbonated drinking water (Koelkebeck et al., 1992) (Table 2). In another study, we showed that hens provided carbonated drinking water had greater tibia bone strength when sampled after exposure to six weeks of heat stress temperatures (Koelkebeck et al., 1993) (Table 3). The work we have done on the use of carbonated drinking water for heat-stressed layers seems to show beneficial results.

In addition to our work with carbonated drinking water, we have explored another avenue of heat stress relief for poultry. Another means of losing body heat in poultry subjected to heat stress temperatures is dissipation of heat through conductive heat loss via the foot pad area. Physiologically speaking the bird reacts to high temperatures by shunting blood towards the skin surfaces to dissipate heat (peripheral vasodilation). Therefore, we hypothesized that if there was a system to remove heat from the birds skin this would effectively help keep the birds body temperature normal. Therefore, we devised a system that allows for conductive heat transfer for broilers subjected to high environmental temperatures. The system is designed to remove body heat by allowing the birds to stand on a water-cooled floor perch, and the perch acts as a heat sink to remove heat (Reilly et al., 1991). The results showed that final body weight and total body weight gain were improved for broilers exposed to heat stress temperatures for 4 wk and provided with a water-cooled roost (Table 4). These results indicated that water-cooled perches may offer a thermoregulatory and performance advantage to broilers exposed to a hot environment.

More recent work in our laboratory has focused on the use of adding supplemental ascorbic acid in the feed and examining its effect on poultry subjected to heat stress and other concurrent stressors at the same time. In the field, when poultry are subjected to one stressor such as heat stress, usually they are also subjected to another stressor at the same time. This results in an additive stress situation which further hampers the ability of the birds to cope with the stress. Since it has been shown previously that ascorbic acid can improve performance of poultry during times of stress, we wanted to examine the stress relieving effect of ascorbic acid on poultry subjected to multiple concurrent stressors (McKee and Harrison, 1995). In this experiment, broiler chicks were exposed to the multiple stressors of beak trimming, coccidiosis challenge, and heat stress from 10 to 17 days of age. Performance parameters and several physiological factors were then measured.

Table 5 shows the effect of ascorbic acid on chick performance, plasma corticosterone, and heterophil:lymphocyte ratios when chicks were exposed to three stressors. These results showed that chicks fed an ascorbic acid supplemented diet (150 ppm) gained more weight than those fed 0 ppm or 300 ppm when exposed to heat stress. Plasma corticosterone was also reduced for chicks fed the 150 ppm level of ascorbic acid compared to those fed 0 ppm and exposed to a coccidiosis challenge or heat stress. Heterophil:lymphocyte ratios decreased for those chicks fed 150 or 300 ppm of ascorbic acid compared to those fed 0 ppm when exposed to either beak trimming, coccidiosis challenge, or heat stress. When the number of stressors were examined simultaneously (order), ascorbic acid supplementation had a positive effect on weight gain and feed intake (Table 6).


In summary, physiological responses of poultry to the environment vary tremendously depending on what type of environmental stressor is imposed. Of the ones discussed herein, temperature, i.e., heat stress, has the most devastating effect on physiological responses and production performance of poultry. The research which we have conducted on ways of alleviating negative effects of heat stress have merit in the commercial poultry industry. Aside from this research, there are some basic practices which a poultry complex manager must follow in order to control in-house air temperatures. The following items should be closely monitored:

  1. Make sure fans operate effectively.
  2. Make sure fans and air inlets are kept clean.
  3. Inspect and/or replace fan drive belts when necessary.
  4. Make sure thermostats and static pressure monitors are operating effectively.
  5. Provide clear cool water at all times.
  6. Don=t overcrowd layers in cages or boilers in a house.

The above list is only a partial list for poultry producers to follow. Following these and many other items will help reduce the devastating effects of heat stress on poultry production performance.

Finally, the commercial poultry industry here in the U.S. has gone to using evaporative cooling type houses as well as the use of tunnel ventilation, especially for broiler houses. If these types of houses are operated properly, then negative heat stress affects on poultry performance should be minimized.


Koelkebeck, K. W., and J. R. Cain, 1984. Performance, behavior, plasma corticosterone, and economic returns of laying hens in several management alternatives. Poultry Sci. 63:2123-2131.

Koelkebeck, K. W., P. C. Harrison, and T. J. Madindou, 1993. Effect of carbonated drinking water on production performance and bone characteristics of laying hens exposed to high environmental temperatures. Poultry Sci. 72:1800-1803.

Koelkebeck, K. W., P. C. Harrison, C. M. Parsons, and G. R. McCain, 1992. Carbonated drinking water for improvement of egg shell quality of laying hens during summer time months. J. Appl. Poultry Res. 1:194-199.

McKee, J. S., and P. C. Harrison, 1995. Effects of supplemental ascorbic acid on the performance of broiler chickens exposed to multiple concurrent stressors. Poultry Sci. 74:1772-1785.

Odom, T. W., P. C. Harrison, and M. J. Darre, 1985. The effects of drinking carbonated water on the egg shell quality of single Comb White Leghorn hens exposed to high environmental temperature. Poultry Sci. 64:594-596.

Reilly, W. M., K. W. Koelkebeck, and P. C. Harrison, 1991. Performance evaluation of heat-stressed commercial broilers provided water-cooled floor perches. Poultry Sci. 70:1699-1703.

TABLE 1. Effect of management alternatives on production characteristics of laying hens1,2

Cage/Floor Density No./Cage or Pen Egg Production Livability Body Weight
(m2/bird)   (%hen-day) (%) (kg)


.116 1 72.3a 98.3a 1.68b
.058 2 74.0a



.039 3 60.3c



.077 3 69.8b



.058 4 70.3ab



.046 5 71.3ab



.039 6 68.1b




.094 51




.187 51




.373 51




a,b,c,dMeans in the same column with different superscript differ significantly (P < .05)

1Average for 10 months of production.
2From Koelkebeck and Cain (1984).

TABLE 2. Effect of carbonated vs tap drinking water on egg production and egg specific gravity1,2

Parameter Treatment Young Hens Old Hens Mean
Hen-HousedEgg Production(%) Carbonated 81.6 71.6 76.8a
Tap 82.8 77.7 80.2a
Mean 82.2a 74.6b  
Egg SpecificGravity(g/cm3) Carbonated 1.0795x 1.0790x 1.0792a
Tap 1.0795x 1.0776y 1.0785a
Mean 1.0795b 1.0783b  

a,bMain effect means within a row and parameter with no common superscripts are different (P < .05).

x,yIndividual treatment means with no common superscript are different (P < .05).
1Means of six replicate groups of 12 hens each per treatment.
2From Koelkebeck et al. (1992).

TABLE 3. Effect of carbonated vs tap drinking water on left tibia bone breaking strength and tibia bone breaking strength per 100 g of body weight1,2

Water Treatment Tibia Bone Breaking Strength
  (kg) (kg/100 g body weight)
Carbonated Water 17.2a .93a
Tap Water 15.4a .79b

a,bMeans within a column with no common superscript are different (P < .05).

1Means of 16 hens each per water treatment.
2From Koelkebeck et al. (1993).

TABLE 4. Effect of water-cooled floor perches on performance of broilers at 51 days of age1,2

Perch Treatment Final Body Weight Total Body Weight Gain
  -- (kg per bird) --
Ambient 2.22b 1.77b
Cool 2.47a 2.02a

a,bMeans within a column with no common superscript are different (P < .05).

1Perch duration was 35 days.
2From Reilly et al. (1991).

TABLE 5. Effects of ascorbic acid supplementation on performance and physiological parameters of chicks exposed to stressors1

    Ascorbic Acid
Parameter Stressor Present 0 150 300
    -- (ppm) --
Weight Gain (g/chick) Beak Trim 223 235 231
  Coccidiosis 207 219 213
  Heat Stress 216b 235a 222b
Plasma Corticosterone (ng/ml) Beak Trim 9.9 6.5 10.5
  Coccidiosis 11.3a 6.9b 10.8ab
  Heat Stress 11.6a 5.5b 9.0ab
Heterophil:Lymphocyte Ratio Beak Trim








  Heat Stress




a,bMeans within a row with no common superscript are different (P < .05).

1From McKee and Harrison (1995).

TABLE 6. Effect of number of stressors imposed simultaneously (order) and ascorbic acid on chick performance1

    Ascorbic Acid
Parameter Stressor Order 0 150 300
    -- (ppm) --
Weight Gain (g/chick) 0 254a 262a 262a
  1 235a 244ab 242a
  2 231a 223b 223b
  3 161by 216bx 224abx
Feed Intake 0 305ay 347y 356ax
  1 297ay 336x 332ax
  2 308a 327 295b
  3 251by 308x 310abx

a,bMeans within a column and parameter with no common superscripts are different (P < .05).

x,yMeans within a row and parameter or with no common superscript are different (P < .05).
1From McKee and Harrison (1995).

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