Karl E. Nestor1, John W. Anderson, and Sandra G. Velleman
The Ohio State University Department of Animal Sciences
Abstract
An experimental line (F) of turkeys was reciprocally crossed with sire lines (designated A and B) from each of two major commercial breeders in order to study the inheritance of carcass traits and body shape. The birds were weighed and killed at 17 weeks of age and various measurements of muscling, leg bones, and body shape were made. Additive genetic variation, as indicated by line differences, was an important source of variation in most traits. The only traits that did not exhibit a line difference in any comparison were weight of the drumstick muscles, tarsometatarsal width, keel length, and Body Depth 2 (body depth at a point 2.54 cm anterior to the posterior end of the keel). Heterosis of live body weight was greater in males than in females. Heterosis in the weight of the Pectoralis major and P. minor muscles was similar to that of live body weight but heterosis in the weight of the leg muscles was higher than that of live body weight. The average heterosis for bone measurements (length of the femur, tarsometatarsal, and tibiotarsal bones and tarsometatarsal width) was very low and ranged from 0.1 to 1.4 %. For measurements of body shape [keel length, Body Depth 1(body depth measured at the cranial process of the keel), Body Depth 2, ratio of Body Depth 1 to Body Depth 2, and length, width, height, and volume of the body cavity], heterosis was low and the average ranged from -3.0 to 2.6 %.
Based on an analysis of both sexes, the commercial sire lines differed in body weight, weights of the P. minor and drumstick muscles, weights of the tarsometatarsal, femur, and tibiotarsal bones, lengths of the tarsometatarsal and femur bones, and various measurements of body shape (Body Depth 1, body depth ratio, and body cavity length, height, and volume). Relative to the commercial sire lines, the F line was smaller, had less breast and leg muscling, and, in general, larger leg bones when sexes were combined. The carcass of the F line was deeper than that of the commercial sire lines when measured at the cranial process of the keel but not at 2.54 cm anterior to the posterior portion of the keel. Body cavity height and body cavity volume were larger in the F line than in the commercial sire lines.
Introduction
The commercial turkey is the result of a cross of a commercial sire line (or sire line cross) and a commercial dam line (or dam line cross). Sire lines are normally selected for improved growth and conformation, whereas selection emphasis in dam lines is for reproduction traits but some selection for growth and conformation is usually done.
The genetic variation in carcass traits and body shape in turkeys has received little attention. Breast width is a measure of the amount of breast muscles (Johnson and Asmundson, 1957). No heterosis in breast width was observed in several crosses involving commercial and experimental lines of turkeys (Nestor, 1971; Ye et al., 1997; Nestor et al., 1997; Nestor and Anderson, 1998; Nestor et al., 2001). The purpose of the present study was to evaluate the genetic variation of carcass traits and body shape in the F, A, and B lines and in reciprocal crosses among them.