Variation in energy expenditures between growing steers with divergent residual feed intakes
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Objectives of this study were to determine if variation in energy expenditures contributed to differences in feed efficiency between low and high RFI steers. Nine steers with the lowest and highest residual feed intakes (RFI) were selected from 169 Braunvieh-sired crossbred steers that were individually fed a pelleted roughage-based diet for 77 d. Following the RFI measurement period, heat production (HP) measurements were obtained using indirect calorimetry while steers were fed the same roughage diet (RD) and on a high-concentrate diet (CD). Linear regression analyses of log HP or retained energy on ME intake were used to determine energy partitioning. Motion and lying activity were measured concurrently with HP on the RD and CD. During the RFI measurement period, low RFI steers had lower (P < 0.01) RFI (-1.7 vs. 1.6 Â± 0.17 kg/d), DMI (7.7 vs. 10.2 Â± 0.42 kg/d) and feed:gain ratio (F:G; 7.2 vs. 10.6 Â± 0.60), but similar final BW and ADG compared to high RFI steers. However, there were smaller differences in DMI (8.4 vs. 9.7 Â± 0.38 kg/d; P < 0.05; 7.56 vs. 8.16 Â± 0.31; P = 0.19) and F:G (10.0 vs. 10.9 Â± 0.40; P = 0.36; 6.5 vs. 7.5 Â± 0.30; P < 0.05) between low and high RFI steers, on the RD and CD, respectively. ME for maintenance (MEm; kg .75 dÂ1) and the partial efficiencies of ME used for maintenance and gain were similar for low and high RFI steers. Likewise, no differences were found in fasting HP or fed HP. Motion activity was lower (P < 0.05) for low RFI steers compared to high RFI steers during fasting HP. Covariate analysis of HP at the same activity level yielded similar results. At slaughter, weights of lung and trachea (P < 0.05), spleen (P < 0.05) and adrenal gland (P = 0.07) were higher for low RFI cattle. The lack of differences in energy partitioning between divergent RFI steers may have been the result of alterations in feeding behavior or stress imposed by adapting steers to calorimetry chambers.
White, Monte Blaine III (2004). Variation in energy expenditures between growing steers with divergent residual feed intakes. Master's thesis, Texas A&M University. Texas A&M University. Available electronically from