Estimations of repeatability and heritability of egg albumen antimicrobial activity and of lysozyme and ovotransferrin concentrations

1. The repeatability and heritability of growth inhibition by egg albumen of two major pathogenic bacteria, a Gram-negative (Salmonella Enteritidis) and a Gram-positive (Staphyloccocus aureus) and of two antimicrobial albumen proteins, lysozyme and ovotransferrin, were estimated in commercial pedigree hens. 2. Repeatability was evaluated in 100 egg-type hens at the beginning, middle and end of the laying cycle on eggs collected for 3 weeks. Heritabilities were estimated at 36 to 40 weeks of age on 400 pedigree hens (2 eggs/hen), which were the offspring of 25 sires each mated with 4 dams. Ovotransferrin and lysozyme were quantified by ELISA. Salmonella Enteritidis (S.E.) and Staphyloccocus aureus (S.A.) were inoculated into a sample of sterilised albumen and enumerated after incubation. 3. Total protein content in albumen decreased with age of laying hens, whereas there were increases in lysozyme or ovotransferrin concentrations and in the bacteriostatic effect of albumen. 4. Repeatability for bacterial growth in albumen ranged from 0.29 to 0.39 for the number of S.E. (log cfu/ml) one day post inoculation (p.i.) but was lower and more variable at 5 d p.i. or for S.A. number. It ranged from 0.27 to 0.38 for S.E. and S.A. number at the mid period of the laying cycle. Repeatabilities were low and variable for total egg albumen protein or lysozyme and ovotranferrin concentrations (0 to 0.22). 5. Negative phenotypic correlations were observed between lysozyme concentrations and S.E. number but that between lysozyme and S.A. number was not significant. 6. Heritabilities were low (0.01 to 0.09) for protein traits. They were 0.11 for S.A. number and 0.16 for S.E. number one day p.i. 7. It appears to be more efficient to select on global bacterial growth than on specific antimicrobial proteins. The most promising trait is the number of S.E. one day p.i.