1. The aim was to assess eggshell contamination in various laying hen-housing systems and to identify factors influencing this contamination.
2. Fifty-eight laying hen farms in France were studied, including 21 flocks housed in conventional cages, 7 in furnished cages and 30 kept on-floor.
3. Sixty eggs per flock were analysed to obtain counts of the total mesophilic flora. Data on equipment and hen management were collected.
4. Mean bacterial count on eggshells tended to be higher in on-floor systems (4.82±0.51 log CFU/eggshell) than in cage systems (4.57±0.58 log CFU/eggshell, P=0.09).
5. Contamination increased with age of the hens, airborne dust concentration, manual packing of the eggs, and packing in plastic rather than in recycled-pulp egg-flats.
6. The effect of the housing system on eggshell contamination, previously described in experimental assays, was confirmed under production conditions.