Phenotypic variation in residual feed intake and performance traits in rams

The objectives of this study were to (1) evaluate relationships in rams between residual feed intake (RFI) and pre-test variables such as birth type and age put on performance test, (2) determine if relationships exist between RFI and carcass characteristics, growth traits, and wool traits in rams, and (3) identify the adequate length of testing necessary to determine individual RFI ranking in sheep. University of Wyoming performance tested rams, whiteface wool breed (WB; n = 183) and meat breed (MB; n = 147), were evaluated for feed intake traits using an automated feed intake system. Whiteface wool breed rams were composed of three contemporary groups (WB1 = Fall 2009, WB2 = Fall 2010, and WB3 = Fall 2011) and MB rams were composed of two contemporary groups (MB1 = Summer 2010 and MB2 = Summer 2011). Carcass, growth, wool, pre-test variables, and weekly weight measurements were collected for rams. Weekly and trial RFI values were calculated separately within each contemporary group. There were no relationships between trial RFI and carcass, growth, or wool traits. However, there was a tendency (P = 0.054) for a positive correlation (0.23) between trial RFI and scrotal circumference in WB2, and a positive (0.46; P < 0.001) and a negative correlation (−0.28; P = 0.068) between belly score and trial RFI in WB1 and WB3, respectively. Weekly variation of RFI estimates was consistent from wk 7 to 15, and was lowest at wk 9 (d 63) for WB rams. The lowest and most consistent weekly variation of RFI in MB rams occurred in wk 5-6, suggesting that a testing period of 40-60 d is sufficient to estimate RFI in sheep. Furthermore, RFI values and RFI rankings generated after wk 6 were consistent throughout the testing period. These preliminary results indicate that RFI is not adversely correlated to carcass, growth, or fleece traits in sheep, and that performance test periods currently used in the University of Wyoming Ram Test are sufficient to estimate RFI.