Effects of ascorbic acid on stress and disease in chickens.

White leghorn chickens were given feed containing 100 mg of ascorbic acid (AA)/kg. One day later, treated chickens and a similar group of unmedicated control chickens were chilled for 1 hour at 6 C, exposed to an unusual sound, fasted, or subjected to rough handling. Heterophil:lymphocyte (H:L) ratios were determined one day later. The AA-treated birds had significantly lower H:L ratios than untreated controls. Chickens that received a diet containing AA had lower H:L ratios than controls (0.86 vs. 1.65) following administration of adrenocorticotropic hormone. Chickens fed a diet containing AA showed increased resistance to a combined Newcastle disease virus-Mycoplasma gallisepticum infection and to a secondary Escherichia coli infection, as well as to a primary E. coli challenge infection. The effects of AA and an antibacterial drug (furaltadone) were additive. In all experiments, the optimum dose of AA was 100 mg/kg of feed. There was a negative correlation between AA level in the diet and feed efficiency.