EGGSHELL CHARACTERISTICS AND PENETRATION BY SALMONELLA THROUGH THE PRODUCTIVE LIFE OF A BROILER BREEDER FLOCK

Egg weight, specific gravity, conductance, and ability of Salmonella t o 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 speci fic gravity and conductance. An additional 10 intact eggs were inocula ted with Salmonella by a temperature differential immersion method for 1 min. Eggs were then emptied of contents and filled with selective m edium that allowed visualization of Salmonella growth on the inside of the shell and membrane complex. Over the 27-wk sampling period, egg w eight 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 li fe of the flock despite the increase in egg weight. Conductance values were not correlated with specific gravity. The number of eggs positiv e for Salmonella penetration after 24 h incubation showed a general up ward trend with flock age; however, penetration frequency and hen age were not found to be significantly correlated (P > 0.05). No relations hip was found between egg specific gravity, conductance, or egg weight and the likelihood of Salmonella to penetrate the eggshell. Because s hell characteristics did not change over time and the penetration patt erns did vary, it is likely that factors other than specific gravity a nd conductance were involved in the penetration of eggshells by Salmon ella.