Effects of supplemental ascorbic acid on the performance of broiler chickens exposed to multiple concurrent stressors.

An experiment was conducted to determine whether ascorbic acid (AA) increases resistance of female Hubbard x Hubbard broiler chicks to multiple concurrent stressors. Stressors imposed from 10 to 17 d posthatch included 2 x 2 x 2 factorial combinations of beak trimming [(B), sham-operated or beak-trimmed and cauterized], coccidiosis [(C), gavage with 0 or 3 x 10(5) sporulated Eimeria tenella oocysts], and heat stress [(H), 28 vs 33 C]. A starter diet was supplemented with AA to provide 0, 150, or 300 ppm (milligrams per kilogram). This resulted in a 2 x 2 x 2 x 3 factorial design with two six-chick replicates of each of the 24 treatment combinations. Data were analyzed using ANOVA and a level of 95% significance. Ascorbic acid increased feed intake and lowered plasma corticosterone and heterophil:lymphocyte ratios. Heat depressed weight gain and feed intake and elevated heterophil:lymphocyte ratios. Heat and AA interacted to improve weight gain and feed intake and lower heterophil:lymphocyte ratios. Coccidiosis depressed weight gain, feed efficiency, and heterophil:lymphocyte ratios. Coccidiosis and AA interacted to increase feed intake and lower plasma corticosterone and heterophil: lymphocyte ratios. Beak trimming increase heterophil:lymphocyte ratios. Beak trimming and AA interacted to increase feed intake and lower heterophil: lymphocyte ratios. Weight gain and feed efficiency decreased whereas heterophil:lymphocyte ratios increased linearly in unsupplemented birds as a function of stressor "order" (the number of stressors imposed simultaneously) indicating an additive effect of systematically increasing the number of stressors. No changes in feed efficiency or heterophil:lymphocyte ratios were detected as a function of stressor order when AA was provided. Ascorbic acid reduced the slope of the regression equation describing the relationship between weight gain and stressor order. It was concluded that AA, particularly at 150 ppm, enhanced performance of broiler chicks exposed to multiple concurrent environmental stressors.