Meeting Abstract
A tetrapod’s body shape determines the position of its center of mass (CoM), and both body shape and CoM can change with age, increases in body weight or gravidity. The domestic turkey has been artificially selected for increased body mass, and a past study reported an altered CoM position. In this study we seek to determine: (1) if muscle groups of the modern domestic turkey have experienced the same proportional increase in size compared to wild turkeys; (2) where the CoM is located in each strain; and (3) how CoM position affects locomotion. We dissected (n= 6 per strain) and grouped muscles by anatomical location (distal hindlimb, proximal hindlimb, trunk and forelimb) and calculated a ratio of muscle mass to total body mass. Only the trunk had a greater mass ratio in the domestic turkey (P= 0.004), driven solely by M. pectoralis (P=0.002), which is strongly selected for breast meat in the poultry industry. We measured the CoM position in 3D using a force plate and biplanar x-rays, and normalized with respect to pelvis length. The CoM was positioned 26% farther anterior to the acetabulum in the domestic relative to the wild turkeys (P=0.009). We assessed locomotion by measuring ground reaction forces as turkeys moved down a trackway with a force plate in the center. Fore-aft force (P=0.001) was lower at any given speed in the domestic turkeys compared to the wild turkeys. A reduction in fore-aft motion is also seen in elderly humans who walk with a more anterior CoM. The mediolateral forces in the domestic turkeys were higher for any given speed (P=0.001) much like obese humans. The change in turkey body shape has led to an anterior shift in the CoM position, and the resulting force pattern mirrors that of humans when mass distribution is altered.
