905
The Effect of Good or Poor Residual Feed Intake Sires on Feedlot Heifer Performance and Carcass Characteristics
Performance and intake data were collected for 90 days on Angus yearling bulls (n = 8) to calculate residual feed intake (RFI) on these potential sires. These bulls were than used as herd sires during the fall breeding season. The Angus x Simmental heifer (n = 84) progeny of these sires were randomly allotted to pens, managed similarly, and fed a common diet. Heifers had intake data collected for 70 days and were weighed every two weeks for calculation of RFI during this period. Thirty-seven heifers were sired by poor RFI (RFI = 0.64 to 1.35) sires and 47 heifers were sired by good RFI (RFI = -0.08 to -0.86) sires. The objective of this study was to observe performance and carcass characteristics of feedlot heifers sired by good or poor RFI sires and determine phenotypic feed efficiency correlations between sire and heifer progeny. Data were analyzed using PROC MIXED procedure of SAS with sire RFI classification (poor or good) as a fixed effect and pen a random effect. Individual animal was the experimental unit. Phenotypic correlations were analyzed with the PROC CORR procedure of SAS. Heifer performance did not differ for initial weight, final weight, or ADG. Heifers sired by good (low value RFI) sires had a 0.65 kg/d lower DMI (P < 0.05) than heifers by poor (high value RFI) sires. As a result, heifers by good RFI sires had a 0.51 kg/d lower RFI than heifers by poor RFI sires. Heifers by good RFI sires also had a desirable 4.4 % increase (P = 0.21) in G:F. Hot carcass weight, rib eye area, backfat, and yield grade did not differ. A 28 unit marbling advantage (P = 0.18) was given to poor RFI sired heifers. Heifer RFI was correlated to DMI at 0.78 (P < 0.05). Heifer RFI and heifer G:F were correlated at -0.27 (P < 0.05); however, sire RFI was not significantly correlated to heifer G:F. Sire RFI was correlated to heifer DMI at 0.33 (P < 0.05). Sire RFI was correlated at 0.47 (P < 0.05) to heifer RFI. The significant correlation of sire RFI to heifer RFI as well as desirable effects on performance and carcass traits assists in the quantification of the advantages of selecting for RFI.
Keywords: sire residual feed intake, heifer performance, feed efficiency