Effects of nutritional management regimen and residual feed intake (RFI) classification on RFI reranking and feeding behaviour for finishing beef steers

Abstract

Over 2 years, 207 steers were fed an alfalfa/corn silage diet to determine growing phase (GP) residual feed intake (RFI) classification (low, medium, and high) for individual cattle. Steers were then allocated to two finishing management regimens (MR): MR 1 cattle gradually adjusted to an 84.7% concentrate (dry matter (DM) basis) diet; MR 2 included backgrounding on pasture before finishing using the same diet as MR 1 cattle. Treatment differences in growth performance were examined using GP and finishing phase (FP) RFI classifications. Based on GP RFI classification, FP average daily gain was greater in MR 2 cattle (P = 0.01) with no RFI classification differences for most FP performance traits. However, low-RFI steers had lower FP dry matter intake (DMI) and greater G:F (P ≤ 0.05) than high-RFI steers based on FP RFI classification. Low-RFI steers had fewer visits to the feeder with a lower eating rate than high-RFI steers in both production phases (P ≤ 0.05). Extensive RFI reranking occurred between production phases with 64.3% of steers changing RFI classification. Given extensive reranking in the present study, RFI classification was poorly repeatable between growing and finishing production phases when diverse diets are fed and does not accurately predict feed efficiency.