Effect of dietary formic and propionic acids on salmonella pullorum shedding and mortality in layer chicks after experimental infection.

This investigation was conducted to study the effect of dietary formic acid (FA) and propionic acid (PA) mixture on inhibitory effect of Salmonella pullorum in layer chicks. Nine equal groups of 1-day-old layer chicks, in addition to positive and negative controls, were fed on day 3 of age with acid-treated feed containing mixture of both acids at concentrations, from 0.5 to 1.5%. Positive and negative controls were fed untreated feed. All groups except the negative control were challenged orally on day 3 with 104 CFU/ml/bird S. pullorum. Cloacal swabs were taken at three successive days and at 7, 14 and 21 days of challenge. After 1, 2 and 3 weeks after challenge, four chicks from each group were killed, and crop and caecal contents were examined for S. pullorum and pH. The numbers of S. pullorum re-isolation from all treated groups, 'except groups treated with mixture of 0.5% and 0.5%, 1% and 0.5% as well as 0.5% and 1% FA and PA', decreased significantly (P < 0.05) compared with the positive control. The mortality rates of all treated groups except the group treated with 0.5% FA and 0.5% PA decreased significantly (P < 0.05) compared with the positive control. The treatment significantly (P < 0.05) lowered the pH of the crop and caecal contents in all groups except the group treated with 0.5% FA and 0.5% PA compared with the control. Also, the treatment significantly (P < 0.05) lowered the pH of the crop and caecal contents in all groups after 3 weeks of treatment compared with the first and second weeks. The treatments significantly (P < 0.05) lowered the frequency of S. pullorum recovery from crop and caecal contents in six groups treated with 1.5 and 0.5, 1 and 1, 1.5 and 1, 0.5 and 1.5, 1 and 1.5, 1.5% and 1.5% FA and PA, respectively. These results indicate that addition of FA and PA mixture in a total concentration of 2% or more to the diet of newly hatched infected layer chicks significantly decreases the crop and caecal colonization by S. pullorum and significantly decreases S. pullorum faecal excretion and reduced the chick mortality rate.