CHANGES IN GROWTH AND BLOOD PARAMETERS IN HEAT-STRESSED BROILER CHICKS IN RESPONSE TO DIETARY ASCORBIC-ACID

Three experiments were conducted to determine whether supplemental ascorbic acid (AA) would alleviate heat-induced deterioration in performance and metabolism of broiler chicks. Day-old female broiler chicks were fed ad lib. on a standard starter feed under either thermoneutral (UH) or heated (H, thermoneutral, heated to 36 degrees C for 6-10 hours per day) conditions to 4 weeks of age. In Experiments 1 and 3 the diet was supplemented with 0, 250, 500 or 1000 mg/kg AA. In Experiment 2, AA was given at 200 mg/kg. In Experiment 1, which started at 7 days of age, heating significantly reduced body growth, feed intake and feed efficiency. AA supplementation, particularly at 250 mg/kg, stimulated growth, intake and efficiency in the H birds but had no significant effect under UH conditions. At both temperatures AA supplementation increased adrenal weight and plasma AA concentration at the end of the experiment. Heating depressed growth, intake, efficiency and adrenal weight in Experiment 2, starting at 1 day of age, while plasma AA levels were increased. AA supplementation increased growth, intake and efficiency of H birds while having no effect under UH conditions. In the third Experiment, starting at 7 days of age, heating reduced growth, intake, efficiency, thyroid weight, and levels of plasma protein, potassium and calcium while increasing body temperature, water intake and plasma glucose, cholesterol and sodium. Under H conditions, AA supplementation alleviated many of these effects, particularly when included at 250 mg/kg. No significant influence was associated with AA supplementation under UH conditions. These data demonstrate that AA, particularly at 250 mg/kg, ameliorates the heat-induced deterioration in performance and metabolism of broiler chicks. AA supplementation of non-heat-stressed birds tends to reduce performance.