Cows were adapted for 7 d to the initial diet. Cows then were weighed full on two consecutive days at the start, at d 42 and at d 84 of the trial to determine gain. Implants were removed 7 d prior to slaughter at the Univer- sity of Illinois Meat Science Laboratory. During the slaughtering-dressing procedure, liver and hot carcass weights were recorded for each animal. At 24 h postmortem, left sides were ribbed and USDA yield and quality grades (USDA, 1975) were determined by University of Illinois personnel. A 15-cm sample of the longissimus muscle was re- moved from the right side immediately poste- rior to the ribbed surface at the 12th rib at 24 h postmortem and frozen (-20~