Residual feed intake (RFI; Luiting and Urff,
1991) and residual maintenance requirement (RMEm;
Romero et al., 2009a) are statistical methods to identify
efficient animals. Laying hens with comparable
BW and egg production vary in efficiency because
of differences in ME expenditures (Luiting and Urff,
1991). In bulls, genetic variation in MEm was closely
associated with genetic variation in energetic efficiency
(Herd and Bishop, 2000).