Feed efficiency and carcass metrics in growing cattle1

Area of Science:

• Animal Science
• Genetics
• Agricultural Economics

Background:

• Traditional feed efficiency metrics like residual energy intake (REI) and residual gain (RG) may not accurately represent production efficiency in feedlot cattle.
• Current definitions often use live-weight as an energy sink, but producers are paid based on carcass weight.

Purpose of the Study:

• To explore alternative definitions of REI and RG that better reflect production efficiency.
• To quantify the relationship between these new definitions and performance, ultrasound, and carcass traits in cattle.

Main Methods:

• Utilized feed intake and live-weight records from 5,172 growing cattle, with carcass data on 2,187.
• Employed animal linear mixed models to estimate heritability and correlations for various REI and RG definitions.
• Analyzed traits including carcass weight, dressing difference, and dressing percentage.

Main Results:

• Heritability estimates for REI traits ranged from 0.36 to 0.50, and for RG traits from 0.24 to 0.34.
• Phenotypic correlations among REI definitions were high (0.90-0.99), but reranking of animals occurred with different definitions.
• Derived RG traits showed weak or no correlation with ultrasound and carcass traits.

Conclusions:

• Alternative REI definitions, such as REICW (using carcass weight) and REICWF (using carcass weight and fat), offer a more accurate measure of feedlot cattle production efficiency.
• Selection based on REICW can improve carcass weight and dressing percentage more effectively than traditional REI.
• While traditional REI is useful for research, REICW and REICWF provide better insights for practical feedlot operations.