PS5-1. Impact of Residual Feed Intake Classification on Performance, Carcass Ultrasound Traits, Feed Intake, Efficiency and Feeding Behavior Patterns in Growing Seedstock Bulls.

Abstract The objective of this study was to characterize residual feed intake (RFI) in growing seedstock bulls, and evaluate associations with feed intake and feeding and drinking behavior patterns. A second objective was to quantify inter-animal variation in RFI associated with feeding and drinking behavior patterns. Across 10 feeding trials, 2,411 growing bulls (Angus, Simmental, South Devon, and composite breeds) were fed in pens equipped with SmartFeedTM and SmartScaleTM systems (C-Lock Inc.) for 56 d to measure daily BW, DMI and feeding behavior traits—including frequency and duration of bunk-visit (BV), meal, and drinking events, time to approach feed bunk following feed delivery (TTB), and day-to-day variation of DMI and feeding and drinking behaviors. Backfat depth was measured at the conclusion of each trial. RFIc was computed as actual minus expected DMI based on regression of DM intake on ADG, mid-test BW^0.75, and backfat depth with trial and breed included as fixed effects. RFIc classification was determined based on ± 0.5 SD from the mean within trial. Low RFIc bulls consumed 24% less (P < 0.01) DMI then high-RFIc bulls, while having similar ADG and BW. Low RFIc bulls had lower (P < 0.01) frequencies and durations of BV and meal events, slower eating rates, longer TTB and lower drinking duration compared to high RFIc bulls. Further, low RFIc bulls had less daily variation in DMI and frequencies and durations of BV, meal, and drinking events indicating more consistent daily feed consumption patterns compared to high RFIc bulls. 36% of variation in RFI was attributable to differences in backfat depth, feeding and drinking behaviors, and daily variances in DMI and behavioral traits. More research is warranted to determine if inclusion of feeding behavior traits will improve accuracy of selection for more feed-efficient cattle.