Effects of growth type on carcass traits of pasture- or feedlot-developed steers

Carcasses of 342 steers of known genetic backgrounds from four fundamentall y different growth types were developed either on pasture or feedlot regime ns to study differences in carcass traits. Growth types were large framed-l ate maturing (LL), intermediate framed-intermediate maturing (II), intermed iate framed-early maturing (IE), and small framed-early maturing (SE). Five calves from each growth type were assigned to each regimen in each year of a:g-yr study. Eighteen steers were removed fi om the study because of acci dent or illness. Data collected. were preslaughter shrunk BW (SBW); hot car cass weight (HCW); chilled carcass weight (CCW); dressing percentage (DRESS ); fat thickness at the 12th and 13th-rib interface (FAT); percentage kidne y, pelvic, and heart fat (KPH); longissimus muscle area (LMA); marbling sco re (MARB); quality grade (QG); and yield grade (YG). Differences in carcass traits reflected genetic differences among growth types. The LL steers had heavier BW, HCW, and CCW and larger LMA (P < .05) than steers of other gro wth types, regardless of development regimen; Among pasture-developed steer carcasses, IE and::SE:steers had higher (P < .05) MARB and QG than either LL or II steers. Carcasses of large framed-late maturing steers had the low est (P < .05) MARB and QG of the growth types. Carcasses of the II, IE, and SE steers had a higher(P < .05) numerical value for YG than carcasses of t he LL steers. Among the carcasses of the feedlot-developed steers, IE and S E steers had the highest (P < .05) MARB and QG. Carcasses from the IE and S E steers were fatter (P < .05)than those from LL or II steers. Carcasses of the LL steers had the lowest percentage of KPH of growth types developed i n the feedlot. No difference was observed in KPH for carcasses of II, IE, a nd SE steers. The LL steer carcasses had the lowest numerical value for YG: of all growth types. These data indicate that variation existed among carca ss traits for the four growth types and that carcass traits influenced by f atness were greater and more attainable in the feedlot-developed steers usi ng current methods of evaluation.