Fattening patterns of yearling steers finished on grain after growth on spring-summer pasture

Hereford (81) and Angus (68) steers were used to determine the effect of feeding time (DOF) and live animal measurements on carcass weight and quality characteristics and fat percentage of certain carcass components. The steers grazed fescue, orchard grass, legume pastures until August, were placed in a drylot and fed whole shelled corn plus protein supplement (36%) and were then serially slaughtered after 0, 28, 56, 84, 112 or 140 DOF. Angus were fed to 112 DOF and Herefords to 140 DOF.

Carcass weight increased linearly from 186.76 kg (0 DOF) to 297.76 kg (140 DOF) for the Herefords and from 171.34 kg (0 DOF) to 283.15 (112 DOF) for the Angus. Mean carcass quality and yield grades of the Herefords at 0, 28, 56, 84, 112 and 140 DOF were average standard, 1.57; high standard, 1.77; high standard, 1.89; low good, 2.71; high good, 2.88; and low choice, 2.68, respectively. Mean quality and yield grades for the Angus at 0, 28, 56, 84 and 112 DOF were average standard, 1.67; high standard, 1.61; average good, 2.10; low choice, 2.38; and low choice, 2.52, respectively.

Regression analysis showed a linear response to DOF in fat percentage of the foreshank, brisket, flank, ribends, loin flap and total sample (Hereford steers). Pat percentage of the chuck and plate showed a quadratic response to increased DOF. At 0 DOF the highest fat percentage was in the plate (24.86%) followed by the brisket (23.35%), loin flap (22.51%), ribends (22.09%), flank (18.24%), total (16.73%), chuck (16.48%), hindshank (15.99%) and foreshank (13.27%). At 140 DOF fat composition in the Hereford steers was highest in the loin flap (42.67%) followed by the ribends (38.11%), plate (36.62%), brisket (34.21%), total (30.62%), flank (30.49%), chuck (28.24%), hindshank (22.32%) and foreshank (16.35%). DOF and steer weight (measured prior to summer grazing) explained most of the variation in fat percentage in the carcass components.

Regression analysis showed a linear response to DOF in fat percentage in the flank (Angus steers). Fat percentage in the flank of the Angus at 0, 28, 56, 84 and 112 DOF was 17.87%; 21.33%; 24.80%; 28.27%; and 31.74%, respectively. DOF and fat thickness over the 12th rib (measured prior to summer grazing) explained the most variation in percentage flank fat.