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Calcium Deficiency and Food Deprivation Improve the Response of Chickens to Acute Heat Stress^1,2,3,

Abdellah Ait-Boulahsen^*,4, Jim D. Garlich^*,,5 and Frank W. Edens^*

^* Department of Poultry Science, North Carolina State University, Raleigh, NC 27695-7608

The tolerance of chickens to acute heat stress may be modified by diet. Broiler chickens fed calcium-adequate (0.90% Ca) or -deficient (0.45% or 0.15% Ca) diets were either fed or not fed for 24 h and exposed to increasing temperatures (from 24 to 41°C). Diets were fed for 7 d before heat stress in Experiment 1 and for 14 d before heat stress in Experiment 2. Body temperature, blood ionized Ca, pH, pCO₂, plasma inorganic phosphate and total Ca were determined. During heat stress, Ca⁺² and inorganic phosphate were depressed in all treatments. Feeding the 0.45% Ca diet for 7 d reduced hyperthermic body temperature of fed chickens but had no effect on body temperature of unfed chickens relative to the groups fed 0.90% Ca. No further improvement in body temperature response to heat stress was obtained by lowering the dietary Ca level to 0.15% or extending the feeding period to 14 d. Food deprivation was more effective in counteracting the heat-induced rise in body temperature than a dietary Ca deficiency. Heat-induced changes in body temperature, Ca⁺², inorganic phosphate and blood pH were highly correlated (P < 0.001). The change in Ca⁺² followed a pattern similar to that of changes in body temperature, but changes in inorganic phosphate seemed to be more indicative of changes in pH. Control birds fed 0.90% Ca exhibited the highest changes in Ca⁺² and body temperature values. Feeding Ca-deficient diets reduced changes in both Ca⁺² and body temperature. Unfed birds, regardless of dietary Ca level, showed the lowest changes in Ca⁺² and body temperature. The results suggest that during heat stress, the increase in body temperature is inversely related to the chickens' ability to maintain blood Ca⁺².

KEY WORDS: • heat stress • acid-base balance • calcium • chickens • food deprivation

¹ Supported in part by a grant from the Southeastern Poultry and Egg Association, Decatur, GA and by the North Carolina Agricultural Research Service.

² A. Ait-Boulahsen was supported by the Minnesota-Morocco Project under the U.S. Agency for International Development.

³ The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service, nor criticism of similar ones not mentioned.

⁴ Current address: Ecole Nationale de Agriculture de Meknes, Meknes, Morocco.

⁵ To whom correspondence and reprint requests should be addressed.

Manuscript received 25 November 1991. Revision accepted 25 August 1992.