Relationships between restricted residual feed intake of Brahman bulls measured in confinement and under different stocking intensities on Coastal bermudagrass pastures
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2016 American Registry of Professional Animal Scientists Efficiency of animal production is an important component of the beef industry. The research objectives of this 2-yr study were to (1) estimate residual feed intake (RFI) of yearling Brahman (Bos indicus) bulls grazing Coastal bermudagrass [Cynodon dactylon (L.) Pers.] using DMI measured with n-alkanes; (2) compare RFI under grazing (RFIg) with RFI determined in confinement under restricted feed intake at 2.8% of BW (RRFIc); and (3) assess the relationships of carcass traits and gastrointestinal tract anatomy to RFIg. Bulls RRFIc-phenotyped as efficient (n-RFI) and inefficient (p-RFI) in both 2009 and 2010 were assigned to 2 replicate pastures at either low or high stocking intensity (STK) for 60 d. In 2009 there was no difference (P > 0.3) between n-RRFIc and p-RRFIc for initial or final BW, ADG, DMI, or feed-to-gain ratio. There was an interaction of RFIg STK (P = 0.043) for ADG in which p-RFIg bulls on low STK had the greatest gain. The p-RFIg bulls had the greatest DMI regardless of STK (P < 0.01). In 2009 differences were found for carcass traits and gastrointestinal tract, and p-RFIg bulls on low STK had the greatest DMI and heaviest gastrointestinal tract. In 2010 p-RRFIc bulls had the heaviest initial BW (P = 0.048), final BW (P = 0.084), and metabolic BW (P = 0.054), and the greatest DMI (P < 0.01). From confinement to pasture, 37.5% of bulls on pasture maintained the same RRFIc rank in 2009, and 56.3% of bulls on pasture remained in the same RRFIc rank in 2010.