Retained Caseous Yolk Sacs Caused by Escherichia coli

An infection of the yolk sac of chickens which was produced by dipping eggs in a suspension of certain isolates of Escherichia coli was described by Reid et al. (1). Infected embryos usually hatched but had higher mortality in the hatcher and during the first 9 days than uninfected controls. The effect was more severe when the eggs were dipped at 18 days than at 1 day of incubation. A large integrated broiler producer reported that many of their birds failed to gain weight at a normal rate and that they lacked uniformity. Condemnation was less than 1%, hatchability was good, and early mortality was low. The only visible lesions were small caseous retained yolk sacs which were at the yolk stalk or umbilicus, or free in the body cavity. From these small yolk masses was isolated a strain of E. coli which was identified by Dr. B. W. Bierer as belonging to serotype 0103.