A two-year study was carried out on the egg productivity in several hen genotypes included in the national poultry gene bank – Barred Plymouth Rock (E strain), White Plymouth Rock (G strain), New Hampshire Red (NG strain), Stara Zagora Red (StR strain), Rhode Island Red (B strain) and Rhode Island White (D strain). The first and second reproductive seasons had a duration of 26 and 28 weeks. All birds were the same age – hatched on June 30th, 2008 and July 2nd, 2009 respectively. The fowls were reared on a farm applying a bio-friendly system with natural day light and free-range coops. The laying started at the beginning of December at 167-169 days of age in the first year and at 151-164 days of age in the second year. The Rhode Island White (D strain) and White Plymouth Rock (G strain) hens were the first to egg-lay. In the two reproductive seasons the hens of the Stara Zagora Red breed (StR strain) had the highest laying capacity, and the hens of the White Plymouth Rock breed (G strain) had the highest egg weight, yolk weight, egg volume and egg surface. The hens of the latter breeds had the highest total egg yield.
In organic poultry production under the bio-friendly system, the temperature and its sharp fluctuations are a powerful environmental factor influencing greatly the egg-laying rate.