Changes in Egg Production and Egg Intervals Under Selection for High Egg Number under 22 our Day Cycles of Artificial Lighting

Data were collected from eight generations of selection for 40 weeks egg production in line UCD-126 of White Leghorns. Hens were kept under a 22 hr day cycle with normal light-dark ratios. Each generation's exact time of lay was recorded for a period of about 30 days for a sample of hens when hens were about 30 weeks old. The percent of time intervals between eggs shorter than 24 hr (“back steps”) were determined for each hen from time-of-lay records. Forty week egg production increased through the selection period of an average of 2.6 eggs per year. There was a correlated response in the percent of ‘back steps,” with an average increase of 1.8% per year. For 40 weeks egg production, the regression of generation means on dams’ cumulative selection differential was .193 and the regression of daughters on their dams was .216. For percent of “back steps,” the daughter-dam regression was very low (.043), but this trait was found to be correlated with 40 week egg production, with the estimates rp = .293 and rg= .308. Some advantages of selecting hens for egg production under short day-cycles of 22 hours instead of using short time-intervals between eggs are discussed.