Background

Millions of dollars have been invested in studying and mapping the bovine genome and diagnostic tools have been developed to predict genetic potential for numerous traits. These tools can be used to select breeding stock with superior genetics for marbling and tenderness. Genetic tools also may be used to sort feedlot cattle upon arrival into outcome groups with carcasses of similar predicted marbling or tenderness. Using growth promotion technologies has significantly reduced beef production costs. Maintaining end-product quality is also important. End-product quality may be improved if DNA marker assisted technology can allow feedlot operators to make more appropriate growth promotion technology decisions.

1. Evaluate the effectiveness of sorting feedlot cattle into marbling or tenderness outcome groups based on DNA marker technology; and 
   
2. Determine if interactions related to end-product quality and palatability exist between predicted outcome group and growth promotion management strategy.
   

Methodology

Findings

Predicted Tenderness
Steers sorted into the HT genotype were 13 lb heavier at the start of the study and 26 lb heavier at harvest than steers sorted into the LT genotypes (Table 1). Average daily gain through most of the study was not affected by tenderness genotype. Dry matter intake day 1-harvest was greater for the HT steers as compared with the LT steers (21.61 versus 20.69 lb/hd-1/d-1). Feed efficiency was not affected by tenderness genotype. Most carcass variables were not affected by tenderness genotype. Hot carcass weight was numerically, but not statistically, higher for the HT steers as compared with LT steers. Shear force was 0.33 kg lower (more tender) for the HT steaks as compared with the LT steaks.

Predicted Marbling
Steers sorted into the HM genotype were 20 lb heavier at the start of the study and 46 lb heavier at harvest than steers sorted into the LM genotype (Table 2). Average daily gain was greater for the HM steers as compared with the LM steers (3.43 versus 3.25 lb/hd-1d-1). Average DMI was greater for the HM genotype steers as compared with the LM genotype (21.60 versus 20.70 lb/hd-1/d-1). Feed efficiency was not affected by marbling genotype. Hot carcass weight was 28 lb heavier for HM steers as compared with LM steers. High marbling carcasses also had greater average yield grade and marbling scores as compared with LM steers. There were no differences in WBSF associated with predicted marbling genotype.

Growth Promotion Strategy
Steers subjected to the AGP were 18 lb heavier at harvest than steers subjected to the MGP (Table 3). From day 1-harvest, DMI was not affected by growth promotion strategy; however, ADG and FG were improved for AGP steers as compared with MGP steers. Hot carcass weight was increased 27 lb for steers assigned to the AGP as compared with MGP. Increased HCW was a function of an increase in dressing percentage for the AGP compared with MGP steers. Average yield grade was lower for the AGP as compared with the MGP. Marbling score and the distribution of USDA quality grades were not affected by growth promotion strategy. Steaks from the AGP carcasses had increased WBSF as compared with MGP steaks.

Implications