Genetic variation in body weight and egg production in an experimental line selected long term for increased egg production, a commercial dam line, and reciprocal crosses between lines

A line (E) of turkeys selected long term (40 generations) for increased egg production was reciprocally crossed with a commercial dam line (BD). The BD line was larger and had better conformation than the E line, but the E line laid more eggs than the BD line. Heterosis was negative and significant for BW at 8, 16, and 20 wk of age (both sexes) and at 50% production (females only). Values for heterosis ranged from -3.1 to -5.5%. Negative heterosis was observed for breast width at 16 wk of age (10.8 and 3.0% for males and females, respectively). Positive heterosis values of 9.2, 10.2, and 11.3% were observed for egg production when based on 84, 120, and 180 d, respectively. Heterosis (-8.2%) 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 180-d production period, heterosis was observed in average clutch length (12.6%) and rate of lay [number of eggs laid: (180 - total days broody)] (8.2%) but not in total days lost from broodiness or the effective length of the laying period (180 minus days lost in periods of 5 or more consecutive days at the end of the laying period). The present results along with those in the literature suggest that more heterosis in egg production traits might be expected in crosses of lines exhibiting extreme differences in BW and body conformation. The negative heterosis in BW in the BD and E reciprocal crosses reduces the commercial importance of such a cross to improve egg production.