Relationship Between Residual Feed Intake and Mitochondrial Function

Abstract Text: Crossbred steers were used to determine if mitochondria complex I (C1) differed among residual feed intake phenotypes (RFI) and if C1 subunits (B-RFI) could account for additional differences in DMI. All experiments were analyzed as a completely randomized design. In Exp. 1 (n=26) and 2 (n=24) steers were fed no-roughage corn-based diets. Steers (n=13) were fed an alfalfa haylage (30% diet DM) based diet during growing phase of experiment three and finished using no-roughage corn-based diets. We hypothesized calf DMI was influenced by metabolic efficiency (RFI) and subsequently C1 subunits could describe additional animal to animal DMI variation. Individual DMI was collected using GrowSafe feed intake system and used to calculate RFI and B-RFI. Band RFI was calculated similar to RFI with DMI as dependent and ADG, metabolic mid weight (MMWT) and C1 subunit (Band3) as independent variables. Blood samples were collected during growing phase of all experiments with an additional sampling during experiment three finishing phase to isolate mitochondria from lymphocytes. Complex I quantities were measured using immunocapture. Complex I subunits were separated into bands using gel electrophoresis and three bands were measured by densitometry. Dry matter intake was less and G:F was greater for –RFI compared to +RFI (P<0.05) steers in all experiments. Band-RFI improved coefficient of determination by 17.04, 1.66, 12.65, 7.12, 12.89, and 2.68 % compared to regressing intake on ADG and MMWT for experiment one, two, growing phase of three, finishing phase of three, and total period of experiment three using mitochondria measurements of growing and finishing phase of three, respectively. In experiment three, RFI was calculated for growing (d 0 to 70) and finishing (d 71 to 140) phases independently and for the total 140 day period. Residual feed intake correlation was 0.14 between growing and finishing phases (P=0.63), 0.79 between growing phase and total period (P=0.001) and 0.65 between finishing phase and total period (P=0.01). Using band 3 in regression equations improved agreement of –RFI from 60 to 75% and +RFI from 57 to 83% between growing phase and total period of experiment three. Growing and finishing phases had 40 and 29% agreement of –RFI and +RFI steers, respectively. In conclusion, mitochondrial complexes accounted for additional variation in intake among steers. Adding band 3 to intake regression equations improved coefficient of determination of all experiments. Residual feed intake phenotype may be influenced by age or cattle growing phase.

Keywords: feed efficiency, mitochondria, residual feed intake