Submitted to: Journal of Animal Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 2/1/1998
Publication Date: N/A
Citation: Interpretive Summary: Genetic antagonisms compromise the efficiency of beef production. An example is the positive genetic association of birth weight and yearling weight. High birth weights are associated with more calving difficulty and calf death loss. Yet, rapid growth leading to high yearling weights is needed for efficient production. Here, a selection strategy for managing this genetic antagonism was evaluated. Selecting bulls based on below average birth weight and high yearling weight simultaneously caused birth weight to remain constant with a 25% sacrifice in growth relative to selecting bulls based on yearling weight alone. The consistency of these results with genetic theory provides added confidence in strategies for managing other genetic antagonisms based on estimated heritabilities and genetic correlations.
Technical Abstract: Mass selection by independent culling levels (YB subline) for below average birth weight (BWT) and high yearling weight (YWT) was compared with single-trait mass selection (YW subline) for high YWT in the inbred population of Line 1 Hereford cattle at Miles City, Montana. There was 4.2 generations of selection in both YB and YW. Heritability estimates for the base population derived from multiple-trait REML were .28 and .31 for direct effects and .16 and .06 for maternal effects on BWT and YWT, respectively. Mid-parent cumulative selection differentials for BWT of YB and YW diverged (-2.9 vs 8.2 kg, respectively), as did the associated genetic trends for direct effects (-.014 kg/yr vs .105 kg/yr, respectively). Mid-parent cumulative selection differential for YWT of YB (102.1 kg) was 64% of that attained in YW (160.7 kg). Likewise, response in YWT of YB (.91 kg/yr) was 61% of response attained in YW (1.5 kg/yr). For both BWT and YWT, maternal genetic trends were similar across selection lines. The genetic potential of YB led to consistently less frequent assistance at parturition than in YW.