Department of Animal Science


Date of this Version



2018 Nebraska Beef Cattle Report. University of Nebraska Extension MP105. Lincoln, NE.


© 2017 The Board Regents of the University of Nebraska.


This study was conducted to evaluate some sources of potential variation in determination of longissimus muscle area between the 12th and 13th ribs of carcasses from heifers fed with or without zilpaterol hydochloride. Cross sections of the rib-loin were taken cranial to the 11th rib and caudal to the 13th rib, about 3–4 millimeters thick at 90 degrees perpendicular to the long axis of the longissimus muscle. Potential variation of longissimus muscle area can arise from the natural variation of muscle size when cutting between the 12th and 13th ribs (up to 9%). Deviation in cutting perpendicular to the long axis of the muscle could contribute 6.9% error. There were no differences in the mean or range of longissimus muscle area among carcasses from heifers fed zilpaterol hydrochloride and controls. These data reinforce the written directions of the USDA to separate the longissimus muscle between the 12th and 13th ribs by a cut as close to 90 degrees as possible.