Residual Feed Intake (RFI) Reranking in Beef Steers Fed Growing and Finishing Diets under Two Management Regimens

A study (factorial design) was conducted to evaluate RFI reranking between growing and finishing phases of production using two nutritional management regimens (MR). One-hundred and eight non-implanted British and Continental crossbred steers (±353 kg) were fed an alfalfa/corn silage growing diet for ~90 days. RFI classification was calculated with steers classified as high, medium, and low (RFI) based on 0.5 SD from the mean. Cattle were allocated to two MR (MR1, MR2) based on RFI, breed, and weight. MR1 cattle were finished on an 84.7% concentrate diet while MR2 cattle were backgrounded on pasture for ~112 days and subsequently finished on the high concentrate diet. Steers were slaughtered at ~750 kg BW. Carcass and meat quality data were collected, and finishing phase RFI calculated to evaluate reranking. Average daily gains (ADG, kg/d) and gain:feed (G/F) respectively included: growing (±1.28; 0.178), MR1 finishing (±1.74; 0.152) and MR2 finishing (±1.92; 0.149). ADG differed between MR (P<0.001 but not amoungst RFI class (P > 0.05), while G/F differed between MR and RFI class (P<0.05). Approximately 74% of cattle changed RFI classification between growing and finishing phases; however, MR did not affect reranking (P=0.65). The odds ratio for reranking based on MR was 0.868, which suggests there is a lower chance of reranking amongst MR. MR2 cattle did however, have a higher proportion (16.7%) of steers rerank from high to low RFI. Spearman rank correlations for RFI reranking were not related to carcass weight (kg), yield (%), lean and fat (%)(P>0.05) while positively correlated with ribeye area (cm2) (P<0.001) and quality grade (P=0.02). Ribeye area was also smaller (P<0.05) for medium RFI steers when compared to either high or low RFI classification. Ultimately, management regimen did not affect reranking of RFI classification for cattle fed a common diet in the growing phase of production.