Genetics of growth and reproduction in the turkey. 16. Effect of repeated backcrossing of an egg line to a commercial sire line

Genetic parameters for clutch and broodiness traits in turkeys (Meleagris Gallopavo) and their relationship with body weight and egg production

The objective of this study was to estimate phenotypic and genetic parameters for clutch and broodiness (BR) traits in turkeys and their relationship with body weight and egg production. Data on dam line hens was available and included: body weight at 18 wk of age (BW18), body weight at lighting (BWL, 29 to 33 wk), age at first egg (AFE), egg number (EN), rate of lay (RL), clutch length (CL), maximum clutch length (MCL), pause length (PL), maximum PL (MPL) and BR. BR was defined as the average number of consecutive pause days between clutches that was higher than the average PL per hen. Heritability estimates for BW18 and BWL were 0.50 and 0.53, respectively. The heritability for egg production, clutch, and pause traits varied from low (MPL = 0.15; BR = 0.15) to moderate (AFE = 0.22; EN = 0.28; RL = 0.29; CL = 0.21; MCL = 0.27; PL = 0.25). Genetic correlations were negative between body weight traits and EN (r_{g (BW18, EN)} = −0.27; r_{g(BWL, EN)} = −0.33) and CL (r_{g(BW18, CL)} = −0.40; r_{g(BWL, CL)} = −0.33). BR was negatively genetically correlated with EN (r_{g(BR, EN)} = −0.85) and CL (r_{g(BR, CL)} = −0.30), and positively genetically correlated with PL (r_{g(BR, PL)} = 0.93) and AFE (r_{g(BR, AFE)} = 0.21). EN had a positive (0.73) and a negative (−0.84) genetic correlation with CL and PL, respectively. Overall, the results of this study confirmed the negative (unfavorable) correlations between egg production and body weight. Despite unfavorable genetic and phenotypic correlations between egg production traits and those relating to BR, the inclusion of BR in a selection program through incorporation of clutch length traits and pause length traits is feasible. Integration of either clutch length traits or pause length traits in a selection index is likely to increase egg number while decreasing broodiness.