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The upper critical ambient temperature in neonatal chicks
W van der Hel1, M W Verstegen, A M Henken
1Department of Animal Husbandry, Agricultural University, Wageningen, The Netherlands.
Insights
Neonatal broiler chicks experience increased body weight loss and water loss as ambient temperatures rise. Their upper critical temperature, beyond which heat loss becomes challenging, is between 36 and 37 degrees Celsius.
Area of Science:
- Animal Physiology
- Poultry Science
- Environmental Biology
Background:
- Neonatal broiler chicks have limited thermoregulatory capacity.
- Environmental temperature significantly impacts chick metabolism and survival.
- Understanding thermal stress is crucial for optimizing broiler production.
Purpose of the Study:
- To quantify heat production, dry matter, and water loss in broiler chicks.
- To determine the effects of constant ambient temperatures (30.8–38.8°C) on chick physiology.
- To identify the upper critical temperature for neonatal broiler chicks.
Main Methods:
- Measurement of heat production, dry matter, and water loss over 24 hours.
- Exposure of neonatal broiler chicks to controlled constant environmental temperatures.
- Analysis of body weight, yolk sac weight, and water loss from the body and yolk sac.
Main Results:
- Increased ambient temperature led to greater total body weight loss.
- Yolk sac weight loss occurred, comprising equal parts dry matter and water.
- Water loss from the chick's body increased significantly above 35°C, and heat production rose with temperature.
Conclusions:
- The upper critical temperature for neonatal broiler chicks is estimated to be between 36°C and 37°C.
- Elevated temperatures induce significant physiological stress, evidenced by increased water loss and weight reduction.
- Heat production decreases with prolonged exposure duration, indicating physiological adaptation or exhaustion.
Abstract:
Heat production, dry matter, and water loss in the body and yolk sac of neonatal broiler chicks were measured during 24 h exposure to constant temperatures from 30.8 to 38.8 C. Average initial body and yolk sac weights were 41.6 and 4.4 g, respectively. Chicks housed at 30.8 C lost 3.5 g/day and chicks housed at 38.8 C lost 5.7 g/day of total body weight. Between 30.8 and 35.1 C, weight loss of the yolk sac was 1.9 g/day. At 38.8 C, weight loss of the yolk sac was 1.4 g/day. Weight lost from the yolk sac consisted of equal amount of dry matter and water. Water loss from the remainder of the chick's body (the total body without yolk sac) increased from 1.8 to 4.4 g as environmental temperature was raised from 30.8 to 38.8 C. This increase occurred mainly above about 35 C. Chick heat production increased with ambient temperature. Heat production as determined per subsequent 3-h period decreased with increasing duration of exposure from 34.6 to 28.2 kJ/kg per hour (1 kJ = .239 kcal) at 30.8 C and from 44.1 to 35.5 kJ/kg per hour at 38.8 C. The upper critical temperature was derived from regression of heat production on temperature. Results showed that this critical temperature was between 36 and 37 C.