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Can DNA marker technology improve feedlot growth promotion management decisions to ultimately improve the consumer's beef eating experience?




Thompson, Katelyn M., author
Wagner, John J., advisor
Engle, Terry E., advisor
Pritchett, James, committee member

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Three hundred and sixty crossbred yearling steers that were sorted from an initial group of 1,100 steers were used to evaluate the effectiveness of sorting feedlot cattle into tenderness and marbling outcome groups based on DNA marker technology and to determine if interactions related to end-product quality and palatability existed between predicted outcome group and growth promotion management strategy. Treatment factors included in the study were tenderness genotype (low versus high), marbling genotype (low versus high), and growth promotion strategy {moderate (Revalor-IS d 1 and d 70) versus aggressive (Revalor-XS d 1 and Zilpaterol supplementation)}. Interactions between tenderness and marbling genotypes and between tenderness genotype and growth promotion treatment were not significant (P > 0.10) for all feedlot performance variables. Steers sorted into the high tenderness (HT) genotype were 5.9 kg heavier at the start of the study (P < 0.05), 11.8 kg heavier at harvest (P < 0.01), and achieved greater DMI (P < 0.05) from d 1 - harvest (9.80 versus 9.38 kg•hd-1•d-1) as compared with the low tenderness (LT) steers. Warner-Bratzler shear force (WBSF) was 0.33 kg lower (more tender) for the HT longissimus steaks as compared with the LT steaks. Steers sorted into the high marbling (HM) genotype were 9.1 kg heavier at the start of the study (P < 0.001), 20.9 kg heavier at harvest (P < 0.0001), and ADG (P < 0.01, 1.56 versus 1.47 kg•hd-1•d-1) and DMI were greater (P < 0.05, 9.80 versus 9.39 kg•hd-1•d-1) as compared with the low marbling (LM) genotype from d 1 - harvest. High marbling genotype carcasses were 12.7 lb heavier (P < 0.05); had greater fat depth (P < 0.06); adjusted fat depth (P < 0.08); higher measured (P < 0.06), adjusted (P < 0.08), and camera adjusted (P < 0.10) PYG; and greater average yield grade (P < 0.09), marbling score (P < 0.05), and camera marbling score (P < 0.05) as compared with the LM genotype. There were no differences (P > 0.60) in WBSF associated with predicted marbling genotype. From d 107 - harvest, steers subjected to the aggressive growth promotion program (AGP) had greater ADG (P < 0.01) and superior (P < 0.001) FG, GF, and NE recovery as compared with steers subjected to the moderate program (MGP). Steers subjected to AGP were 8.2 kg heavier (P < 0.06) at harvest and had 12.2 kg heavier (P < 0.05) HCW and greater (P < 0.01) dressing percentages than steers subjected to MGP. From d 1 - harvest, ADG (P < 0.05), FG (P < 0.01), GF (P < 0.01, and recovered NEm and NEg (P < 0.05) were improved for AGP as compared with MGP steers. Camera adjusted PYG (P < 0.07), calculated yield grade (P < 0.05), and camera yield grade (P < 0.05) were lower and grader LM area (P < 0.01) and camera LM area (P < 01) were greater for AGP as compared with MGP carcasses. Marbling score and the distribution of USDA quality grades were not affected by growth promotion strategy. Aggressive strategy steaks had increased (P < 0.01) WBSF as compared with MGP steaks. Interactions between marbling genotype and growth promotion strategy suggest that steers categorized as HM genotypes did not respond to Zilpaterol to the same degree as LM genotypes. Three-way interactions for USDA yield grade distribution indicated that for HT - LM and the LT - HM steers, AGP had limited impact on the percentage USDA yield grade 3 carcasses but reduced the percentage USDA yield grade 4 carcasses as compared with MGP. Yearling steers can successfully be sorted into marbling or tenderness outcome groups based on DNA marker technology. Tenderness can be improved by using MGP as compared with AGP; however, growth promotion strategy did not impact marbling or USDA quality grade distribution and few interactions related to end-product quality and no interactions for WBSF existed between predicted outcome group and growth promotion management strategy indicating that the degree that end product quality is impacted by growth promotion strategy is largely independent of marbling and tenderness genotype.


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