FEEDLOT PERFORMANCE AND IMMUNOLOGY OF BEEF STEERS FED A LOW VITAMIN A DIET AND SELECTED FOR ADH1C GENOTYPE

Abstract

Prior nutrigenetic studies on the interaction between limiting vitamin A (VA) and the ADH1Cc.-64T>C SNP have shown that TT animals with reduced VA intake have improved intramuscular fat (IMF) in the longissimus thoracis muscle in beef cattle. The intent of this study was to determine whether this marker-assisted management (MAM) strategy would be effective at a commercial level, and whether there would be any immune function ramifications from limiting dietary VA. This occurred in two separate experimental groups, the first being a smaller immunology population, and the second in a large-scale commercial feedlot. Crossbred steers (n = 18), black in colour, were selected from a prior feeding trial so that all combinations of ADH1C genotype (TT, CT, and CC) and VA level (25% or 75% of NRC, 1996 recommendations) were equally represented. Blood cell count analysis, peripheral blood mononuclear cell (PBMC) proliferation and stimulation assays, and quantitative reverse transcription polymerase chain reaction (qRT-PCR) examination of cytokine expression were conducted and compared. Vitamin A did not affect any of the measured parameters, and any significant (P < 0.05) pen and genotype effects did not equate to clinically ill animals. The second study population included 2000 mixed breed beef steers, separated into 40 feedlot pens. Genotype at ADH1C (TT or CT), VA level (50% or 100% of NRC, 1996 recommendations), and implant status (IMS; implanted or non-implanted, IMP or NI respectively) were all equally represented with 5 pens of each possible combination of variables. Production and carcass data were collected, and the expected VA X ADH1C interaction effect was not observed. An IMS X ADH1C interaction effect was observed with average daily gain (ADG; P=0.03), and IMS alone had significant effects on dry matter intake (DMI; P<0.01), total days-on-feed (P<0.01), USDA yield grade (P<0.01), marbling score (P<0.01), rib-eye area (REA; P=0.01), and backfat thickness (P<0.01). Overall, IMP animals finished on fewer days-on-feed with higher ADG, DMI, and REA and lower yield grades, marbling scores, and backfat thickness. No other interaction or main effects were observed, suggesting that the ADH1C X VA nutrigenetic MAM strategy is not effective at a feedlot level at this time.