Submitted to: Journal of Animal Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: May 15, 2002
Publication Date: July 1, 2002
Citation: Bennett, G.L. 2002. Live weights and carcass traits of steers from heifer calving ease selection and control lines [abstract]. Journal of Animal Science. 80(Supplement 1):322. (Abstract #1285) Technical Abstract: Intense selection since 1992 for reduced heifer calving difficulty score EPD and average yearling weight EPD in seven experimental populations of cattle has resulted in improved heifer calving ease, lighter birth weight, and similar yearling weight EPD compared to control lines. Control lines were selected for average birth weight and yearling weight EPD. This apparent genetic change in growth pattern might alter carcass composition. Females born in 1996 and 1997 were randomly retained within the two lines of each population. They were mated to sires from their own lines and produced calves as 2- and 3-yr-old cows in 1998 and 1999. Random (stratified by sire and dam) male calves from select (N = 204) and control (N = 91) lines were fed as steers and measured for live weights and carcass traits. The 295 calves were from 157 sires and 279 dams. Birth weights were 4.5 kg (11.3%) lighter in the select lines (P<0.001). Weight differences (select - control) were small and not significant at weaning (1.4 kg) and at subsequent average ages of 261 d (2.3 kg), 368 d (1.1 kg), and 436 d (-1.7 kg). Carcass weight was also similar (824 vs 825 kg). Adjusted fat thickness was greater (P<0.01) in select lines (0.91 vs 0.78 cm) and marbling score was slightly higher (P<0.10). Differences in ribeye area and KPH% were small and not significant. Results show that selection for calving ease and average yearling weight produced calves that were lighter at birth but had weights similar to control calves from weaning to 14.5 mo of age. Select animals following this genetically determined growth pattern may be slightly fatter.