Student Competition : Animal Well-Being and Behavior 49 Locomotor biomechanics and muscle force performance in wild and domestic turkeys

Wild turkeys provide an opportunity to understand how increased muscle mass influences the locomotor performance of domestic turkeys. This study’s goal was to identify differences in muscle distribution patterns, quantify the locomotor capabilities, and assess the capacity for muscle force production in both strains of turkey . Male and female wild (n = 6) and domestic (n = 6) turkeys were dissected, and mass of the hindlimb, forelimb and pectoral muscles was measured to establish differences in muscle distribution. The pectoralis superficialis was the only muscle that was significantly larger in the domestic turkey when normalized to body mass (P = 0 .004) . However, when normalizing with ratio of muscle mass to the length3 of the tibiotarsus, all of the muscles were significantly larger in the domestics than in the wild strain. This indicates that domestic turkeys are supporting far more muscle mass on a largely similar skeletal frame . To obtain ground reaction forces and gait kinematics, turkeys (n = 10) of each strain, walked across a force plate . The average speed of the domestic turkeys was very slow, 0 .48 m/s, compared with the wild turkeys, 1 .93 m/s . The average peak vertical force of the domestic turkeys was 1 .04 times body mass, less than half the wilds’ vertical force . The domestic turkey also displayed higher mediolateral forces (P = 0 .001, SMATR) . These low and slow ground-reaction forces may be due to the muscle contractile capabilities . To test for possible effects of muscle-force capacity, an in situ preparation of the lateral gastrocnemius (LG) muscle in the domestic turkeys (n = 6) allowed comparison with past studies on wild turkeys . The domestic LG muscle produced 21% less force than wild strain (P = 0 .048), (mean muscle force of 31 .8 N/cm2 versus wild mean force of 40 .3 N/cm2) . However, the maximum velocity was high in domestic turkeys at 21 .5 L/s, compared with 13.0 L/s in the wilds. These results indicate that artificial selection for increased body mass results in low maximum speeds and low ground reaction forces, which may be partially due to changes in the contractile performance of the hypertrophied muscle tissue .