The objective of this study was to determine if selection for increased breast muscle mass has affected the supracoracoideus muscle's ability to regulate pH during physical activity in turkeys. The lightweight male line (LM) had the greatest breast muscle mass as a percent of body weight (p<0.0001), a lower average pH (6.68; p<0.0001), and greater Lactate Dehydrogenase (293 mmol NADH min -1 µg -1 ; p<0.0001) and Glyceraldehyde Phosphate Dehydrogenase (0.4452 mmol NADH min -1 µg -1 ; p<0.05)

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... vities than the HM and FL lines. The LM line had the highest ratio (2.33:1)(p<0.05) of adult to neonatal myosin. Hens had greater breast muscle mass as a percent of body weight than males (p<0.0001), and a lower average pH (6.62; p<0.05). This study showed that genetic selection for breast muscle mass resulted in an increased ratio of adult to neonatal myosin and an increased anaerobic capacity, which may predispose birds to a lower ultimate pH during physical activity. iii ACKNOWLEDGMENTS First, I would like to thank GOD for allowing me the opportunity to partake of this experience. I would also would like to give thanks to his son, Jesus Christ, for giving me the strength to deal with the adversity and trials of everyday life and higher education. I am truly thankful for the support of my wife, Jessica, and the rest of my family during my studies as a master's student.