Comparison of white and brown egg shell laying stocks

Abstract

Four consistent stock brand names of white egg shell laying fowl were compared with four such stocks laying brown shelled eggs. Data were derived from the Combined Summaries of European Random Sample Egg Production Tests (ERSEPT) 1979–1992 and from the North Carolina Layer Performance and Management Test (NCLPMT) 1984–1992. In the former, laying performance was recorded from 141 to 500 days of age and the data were based on annual means derived from about six testing stations, while the latter involved one testing station with recording over two cycles of production from 140 to 434 days and from 435 to 728 days (which included a moult). Although identical stocks were not available in both continents, results for egg mass show a similar initial superiority for the white egg shell stocks. This advantage decreased over the years and changed to an advantage for the brown egg stocks of about 0.5 kg in the ERSEPT and 1.1 and 0.7 kg, respectively, in the first and second cycles of the NCLPMT. In the ERSEPT the white egg stock advantage in terms of feed to egg mass ratio decreased. This can be attributed to greater genetic gains by the brown egg stocks whose final body weight declined (from 510 g to 270 g above that of the white egg stocks); increased mean egg weight (with the gap between the stock types widening from 2.3 to 3.3 g); and to some extent, earlier sexual maturity, as indicated by decreased age at 50% production. Results of the NCLPMT also show that the improved egg mass for the brown egg stocks was achieved by closing the gap in hen-housed production (20 eggs per bird) while maintaining an egg weight superiority of 3.4 g. The improvement in performance was particularly evident in the first production cycle. In the second cycle the brown egg stocks showed higher mortality rates, together with increased food consumption and a smaller egg size advantage. In both production cycles the brown egg stocks were characterized by much higher levels of meat spots.

Keywords::

• Brown
• colour
• eggs
• Europe
• performance
• production
• random sample tests
• USA
• white