Genetics of growth and reproduction in the turkey. 15. Effect of long-term selection for increased egg production on the genetics of growth and egg production traits.

A line (E) of turkeys selected long-term (37 generations) for increased egg production was reciprocally crossed with its randombred control population (RBC1) that served as the base population of the E line to study the influence of long-term selection on the development of nonadditive genetic variation for egg production and body weight traits. Heterosis was significant for BW at 8, 16, and 20 wk of age and at 50% production (females only). At 16 and 20 wk of age, heterosis for BW was significant only for male offspring. No heterosis was observed in the reciprocal crosses for egg production when measured for 84, 180, or 250 d. Heterosis was significant for rate of response to stimulatory lighting of 14 h light per day (days from stimulatory lighting to production of first egg). Based on data for a 250-d production period, heterosis was observed in average clutch length but not in total days lost from broodiness or the effective length of the laying period (250-d lost in periods of 5 or more consecutive d at the end of the laying period). The present results suggest that long-term selection for increased egg production and the correlated decrease in BW increased the relative nonadditive genetic variation in BW. Reciprocal effects were significant for BW at 8 and 16 wk of age, probably due to a large difference in egg weight between the E and RBC1 lines.