SUMMARY

GeneSTAR^® Quality Grade is a DNA genetic marker panel test comprised of four markers (QG1 (TG5), QG2 (M2), QG3, and QG4). Results from the GeneSTAR^® Quality Grade test were found to have a significant association with marbling score and quality grade (% of animals grading choice or prime)¹ in a combined Bos taurus sample population of 747 animals.  This test was not validated on a Bos indicus-influenced or purebred Bos indicus population.

The average effect of a GeneSTAR Quality Grade star was a 6.5 increase in marbling score and a 4.25% increase in the number of cattle grading choice or better, although as indicated by the scattered solid point values on the above graph, the actual value of a star will differ depending upon which marker is generating the star and the allele frequency of the marker. Although it is theoretically possible to get animals with 8 stars, the combined sample population of 747 animals included only 5 animals with more than 4 stars (four 5-star, one 6-star, and no 7 or 8-star animals) so it is difficult to derive estimates for these genotypes. Breeders should realize that the actual increase in % grading choice and prime in a given situation will also depend upon a number of environmental and other factors including the proportion of the herd grading choice and prime.

¹ Quality Grade (% choice) was analyzed as an “all or none” trait (each animal was either USDA Choice or better, or it was not). Such traits have the property that the size of the effect is quite dependent on the population mean. This does not reduce the ability of the test to rank animals correctly, but it does complicate the interpretation of the effect sizes. The size of effect is greatest in populations that grade approximately 50% Choice or better, but can be much lower in populations with either a high or low proportion of animals that grade Choice or better.