Abstract
The objective of this study was to evaluate the relationship between skeletal muscle mitochondrial function and residual feed intake (RFI) in growing beef cattle. A 56 day feeding trial was conducted with 81 Angus crossbreed steers (initial BW = 378.4 ± 43.3 kg) from the Sierra Foothill Research Station (University of California). All individuals were fed the same finishing ration (ME = 3.279 Mcal/kg DM). ADG, DMI, and RFI were 1.82 ± 0.27, 8.89 ± 1.06, and 0.00 ± 0.55 kg/d, respectively. After the feeding trial, the steers were categorized into high, medium, and low RFI groups. Low RFI steers consumed 13.6 % less DM (P < 0.05) and had a 14.1% higher G:F ratio (P < 0.05) than the high RFI group. No differences were found in age, ADG, nor BW (P > 0.10). The most extreme individuals from the low and high RFI groups were selected to measure mitochondrial function (n = 5 low RFI and n = 6 high RFI). Mitochondrial respiration was measured using an Oxygraph measurement system from Hansatech Instruments. State 3 and State 4 respiration rates were similar between both groups (P>0.10). Comparing the groups according to age by analysis of covariance, low RFI steers have shown greater respiratory control ratios than high RFI animals, with mean ratios of 4.95 and 4.23, respectively (P = 0.037). This data suggests that the muscle mitochondria of low RFI cattle show greater coupling between respiration and phosphorylation than high RFI animals.