Eggshell characteristics and penetration by Salmonella through the productive life of a broiler breeder flock

Egg weight, specific gravity, conductance, and ability of Salmonella to penetrate the shell and membranes were determined for hatching eggs from a commercial broiler breeder flock. Thirty unsanitized eggs were sampled on Weeks 29, 34, 39, 42, 48, 52, and 56 of flock age for specific gravity and conductance. An additional 10 intact eggs were inoculated with Salmonella by a temperature differential immersion method for 1 min. Eggs were then emptied of contents and filled with a selective medium that allowed visualization of Salmonella growth on the inside of the shell and membrane complex. Over the 27-wk sampling period, egg weight increased from 56 to 66 g and was positively correlated with hen age (r = 0.96, P < 0.05). However, neither specific gravity (ranging from 1.077 to 1.082) nor eggshell conductance (ranging from 14.7 to 17.9 mg weight loss/d per torr) showed any clear trend throughout the life of the flock despite the increase in egg weight. Conductance values were not correlated with specific gravity. The number of eggs positive for Salmonella penetration after 24 h incubation showed a general upward trend with flock age; however, penetration frequency and hen age were not found to be significantly correlated (P > 0.05). No relationship was found between egg specific gravity, conductance, or egg weight and the likelihood of Salmonella to penetrate the eggshell. Because shell characteristics did not change over time and the penetration patterns did vary, it is likely that factors other than specific gravity and conductance were involved in the penetration of eggshells by Salmonella.