Effects of Size and Rate of Maturing on Carcass Composition of Pasture- or Feedlot- Developed Steers*

Steers (n = 335) of known genetic backgrounds from four fundamentally different growth types were subjected to two production systems to study the main effects and possible interactive effects on carcass composition. Growth types were animals with genetic potential for large mature weight (LL), intermediate mature weight-late maturing (IL), intermediate mature weight-early maturing (IE), and small mature weight-early maturing (SE). Each year, in a nine year study, calves of each growth type were weaned and five steers of each growth type were developed on pasture or feedlot and harvested at approximately 20 and 14 mo of age, respectively. Data recorded were chilled carcass weight and percentages of forequarter, foreshank, chuck, rib, plate, brisket, hindquarter, round, rump, shortloin, sirloin, flank, lean, fat, bone, and retail cuts. The growth type×production system interaction was an important source of variation in chilled carcass weight (p = 0.0395) and percentage retail cuts (p = 0.001), lean (p = 0.001), fat (p = 0.001), rump (p = 0.0454), shortloin (p = 0.0487), and flank (p = 0.001). The ranking of the growth type x production system means for percentage lean was LL-pasture>IL-pasture = IE-pasture = SE-pasture>LL-feedlot, IL-feedlot>IE-feedlot = SE-feedlot. The growth type× production system interaction was non-significant (p>0.05) for forequarter, foreshank, chuck, rib, plate, brisket, hindquarter, round and bone. Growth types of IE and SE yielded greater (p<0.05) mean forequarter than did growth types of IL and LL (51.6±0.3 and 51.5±0.3 vs. 51.1±0.3 and 50.8±0.3%). Mean bone was highest (p<0.05) for the LL growth type and lowest (p<0.05) for the SE growth type (19.5±0.5 vs. 16.8±0.5%). Mean bone was greater (p<0.05) for the pastured steers than for the feedlot steers (21.8±0.8 vs. 14.5±0.6%). These data indicate that growth type responded differently in the two production systems and that these results should be helpful in the match of genetics to production resources. (Asian-Aust. J. Anim. Sci. 2006. Vol 19, No. 5 : 661-671)