K. E. Nestor1, J. W. Anderson, and R. A. Patterson
The Ohio State University Department of Animal Sciences
Bilateral asymmetry is a measure of developmental stability. At 20 weeks of age, the right and left shank length, shank width (width laterally at the dew claw), shank depth (width perpendicular to the dew claw), and face length (between auditory canal opening and the posterior junction of the upper and lower mandible) were measured in three randombred control and three selected lines of turkeys. The lines were grown intermingled, with the sexes being grown in different houses. The selected lines had been selected for increased egg production (38 generations), increased 16-week body weight (32 generations), or increased shank width (19 generations) and had a higher level of inbreeding (average = 36.9%) than the randombred controls (average = 11.6%). The bilateral differences (right minus left) were analyzed for the presence of asymmetry. In order to adjust for possible scaling effects, relative asymmetry (RA), in which the mean of the absolute differences between sides was divided by the mean of the two sides and the resulting value multiplied by 100, was used as a measure of bilateral asymmetry. The randombred control and selected lines were contrasted to study the effect of homozygosity on RA. Likewise, the large-bodied lines (F, FL, and RBC3) were contrasted to the small-bodied lines (RBC1, E, and RBC2) to study the effect of body weight on RA.
The level of asymmetry for the traits was ranked: face length > shank width = shank depth > shank length. The individual lines differed in RA for shank length and shank width for both sexes and for shank depth and face length in females. In general, the influence of body weight, as measured in the contrast of large-bodied and small-bodied lines, on RA was larger than that of homozygosity, as measured by the contrast of the selected and randombred control lines.
1 For more information, contact at: The Ohio State University, Ohio Agricultural Research and Development Center, 125 Gerlaugh Hall, 1680 Madison Avenue, Wooster, OH 44691, 330-263-3757, Fax 330-263-3949, e-mail: nestor.1@osu.edu