Genetics of growth and reproduction in the turkey. 12. Results of long-term selection for increased 180-day egg production

A line of turkeys selected 28 generations for increased 180-day egg production (E) was compared through regression analysis with the randombred control population (RBC1) from which it originated. The only curvilinear trends observed for RBC1 were for egg weight and 8-wk (both sexes) and 16-wk (males) BW. Linear declines in egg production and rate of lay through 84 and 180 days of lay, the member of clutches during the 180-day production period, effective days of egg production, and 16-wk (females) and 20-wk (both sexes) BW were observed for RBC1. The RBC1 turkeys had linear increases in the percentage of broody hens during the first 84 and 180 days of production, the average length of the broody period, and the total number of days lost to broodliness during the 180-day period. When expressed as a deviation from RBC1, positive quadratic curvilinear changes were observed for E turkeys for number of clutches and broody periods, and days lost to broodliness during the first 180 days of production. Percentage hatch of fertile eggs at 8 and 12 wk of production also exhibited a positive quadratic change with generation. Linear increases in egg production, rate of lay, clutch length (average and maximum), number of effective days of production, and percentage hatch of fertile eggs 12 wk into production were observed for E turkeys. There were linear declines in number of days from photostimulation to the production of first egg, number of clutches, add number, average length, and days lost to broodiness for E line turkeys. The E line had the same fertility at 8 wk of production and broody periods of the same duration as RBC1 turkeys. Body weight of E turkeys declined in later generations of selection, as indicated by curvilinear response of 8- and 16-wk BW and linear decline in 20-wk BW. Although there appeared to be a plateau in the response to selection for 180-day egg production, selection response was being masked by environmental influences.