Efficacy of a Thyroglobulin Dna Marker for Marbling in Explaining Variation in Carcass and Perfomance Traits of Early-weaned Simmental Steers

Research has demonstrated that triiodothyronine and thyroxin have been associated with marbling deposition in Wagyu beef. Thyroglobulin 5 (TG5) polymorphism has been associated with an improvement in overall fattening and could be used as a “gene marker” for marbling. The commercially available GeneSTAR Marbling test measures the specific polymorphism in DNA as either having zero, one, or two copies of the gene; identified as 0-STAR, 1-STAR, or 2-STAR, respectfully. Early-weaned Simmental steers (n = 175, 3⁄4 Simmental or greater) of known genetics were individually fed over a four-year trial period to determine correlations between GeneSTAR Marbling test results and intramuscular fat deposition. The American Simmental Association provided sire and maternal grandsire Expected Progeny Differences (EPDs) for yearling weight (YW), marbling (MARB), percent retail cuts (PRC), and carcass weight (CW) allowing EPD calculations to be made for each steer. Steers were weaned at 88.0 ± 1.1 d and fed a high concentrate diet for 84.5 ± 0.4 d prior to allotment. Steers were subsequently fed a 90% concentrate, whole shelled corn and corn silage diet, supplemented to contain 15.5% CP using SBM for 249.7 ± 0.7 d and harvested at 423.3 ± 1.4 d. DNA samples were used by Genetic Solutions Pyd Ltd (Australia) for GeneSTAR Marbling analysis. Marker frequencies 0-STAR (n = 47), 1-STAR (n = 95), and 2-STAR (n = 33) had no affect (P > 0.10) on marbling score, longissiumus dorsi area, 12 rib fat thickness, dressing percent, quality grade (QG), or yield grade (YG) . There was a numerical (P > 0.10) increase in percent Low Choice or higher, 83.0%, 87.4% and 90.9% for the 0-STAR, 1-STAR and 2-STAR steers, respectively. The percent average Choice or higher was respectfully 42.55%, 44.21% and 30.30% (P > 0.10) for the three marker populations. No differences (P > 0.10) among performance parameters were due to the frequency of the GeneSTAR marker. In addition, GeneSTAR results were not found to be associated (P > 0.10) to MARB; however, there was a linear increase (P < 0.10) in YW and CW. There was a very strong (P < 0.0001) correlation between GeneSTAR and PRC (r = -0.81) but no correlation (P > 0.10) between the marker test and marbling score, chemical IMF percent, or QG determined by USDA or University of Illinois grader. GeneSTAR tended (P < 0.10) to be correlated to ultrasound YG (r = 0.21). These data suggest the potential for a management system by GeneSTAR marker interaction where early-weaning on a highenergy may dilute the effects of the marker.