Characterization of energetic efficiency in adult broiler breeder hens

This trial characterized residual feed intake (RFI) and residual maintenance requirement (RME(m)) as measures of energetic efficiency in broiler breeder hens. The RFI was defined as the difference between observed and expected ME intake and RME(m) as the difference between observed and expected maintenance requirements. A total of 600 Ross 708 1-d-old pullets were placed in floor pens. At 16 wk, 144 hens were caged and randomly assigned to 1 of 2 feed allocation treatments (72 birds each). The control treatment had feed allocated on a group basis (GRP) following the standard BW target. A second treatment had feed allocated on an individual-bird basis (IND) and followed the same BW target as GRP. Sexual maturity age, egg and chick production, and several feed conversion ratios were correlated to standardized efficiency indices of RFI (SRFI) and RME(m) (SRME(m)) in each treatment. Greater SRFI and SRME(m) values described a greater energetic efficiency. Residual feed intake was more variable in IND than GRP hens (P < 0.001). The variability of RME(m) did not differ between treatments (P = 0.14). The SRFI was positively correlated to egg production in the GRP hens (r = 0.31), but negatively correlated in IND hens (r = -0.40) and was correlated to feed conversion per chick only in the GRP-based feed allocation (r = -0.44). The SRME(m) correlated strongly to egg production (r = 0.64), chick production (r = 0.64), and feed conversion per chick (r = -0.59) in both feed allocation treatments. Feed intake confounded the RFI calculation, which limits the value of RFI as a selection criterion in meat-producing animals. The independence of RME(m) from feed intake is desirable for energetic efficiency assessment in selection programs because consistent values can be obtained across different management schemes. Hens with lower maintenance requirements (greater RME(m) efficiency) partitioned more energy toward reproduction than did high-maintenance hens. The RME(m) methodology provided an unbiased estimate of energetic efficiency by adjusting the maintenance requirement for the effect of dietary thermogenesis.