GENETICS OF GROWTH AND REPRODUCTION IN THE TURKEY .13. EFFECTS OF REPEATED BACKCROSSING OF AN EGG LINE TO 2 SIRE LINES

The objective of the present study was to determine the feasibility of rapidly increasing the BW of dam lines by repeated backcrossing of a dam line to a sire line. A line (E) selected long-term for increased e gg production was backcrossed to a line (F) selected long-term for inc reased 16-wk BW (BC1) and to a commercial sire line (BC2). The BW of t he F and commercial sire lines were about twice as large as that of th e E line. Egg production of the E line was more than double the egg pr oduction of either of the sire lines. Large gains in BW and breast wid th were observed in both backcrosses. Based on additive genetic variat ion, gains in BW were less than expected in the first generation for f emales in the BC1 and for both sexes in the BC2. Values observed for m ales of the BC1 were similar to expected values at 8 and 16 wk and lar ger than expected values at 20 wk of age. Slower than expected BW gain s in Generation 1 may have been attributable to the small egg size of E females. After Generation 1, BW at 16 and 20 wk of age were equal to , or greater than, expected. Egg production was reduced in both backcr osses relative to the E line. Fertility and hatchability were reduced relative to the E Line by backcrossing in BC1 but not in BC2. Results of the present study suggest limited repeated backcrossing of a dam li ne to a sire line may be an economically feasible method to greatly in crease the BW of dam lines without unduly sacrificing reproduction cap ability.