Posted October 29, 2024
By Tom Brink, RAAA CEO
Even if two beef animals have the same sire and dam (full siblings), their genetics can be significantly different. The DNA “shuffle of the cards” that takes place at conception can result in billions of possible genetic combinations. To seedstock cattle breeders, this means that closely related animals often end up with distinct genetic differences in economically important traits. Among full sibs, we may see one that ranks considerably higher (or lower) than the other for virtually any EPD trait.
For example, consider two young, flush mate 1A Red Angus females, born two days apart. Both sisters DNA parent verify to the same sire and same dam. Yet, because they are genotyped, their genomically-enhanced EPDs depict sizable genetic differences in multiple traits (see table below). They are not the same DNA-wise. Nor do they look the same phenotypically. Most breeders would select Full Sib B, if appearance was all that was being considered.
EPD and Index Differences. For starters, the two sisters’ Birth Weight EPDs are separated by 3 pounds (-4.0 versus -1.0), differentiating their corresponding percentile ranks for Birth Weight from the top 14% of the breed to the bottom 39%. Ribeye Area EPDs between these two full sibs show an even greater difference – bottom 6% to the top 13%. Carcass Weight EPD rankings range from the top 16% to the bottom 7%, which is pretty much from one end of the Red Angus bell curve to the other.
There are other traits that are more similar between the two females. Stayability, for example, only varies by one point (14 vs. 15). However, more than not, the genetic differences across multiple traits are substantial, and this affects their indexes too. ProS ranges from the bottom 5% to the top 39%, indicating that one of the two full sisters has considerably more overall genetic merit. Full Sib B won the genetic lottery when compared to her full sister.
This comparative exercise also underscores the value of genomic testing. Pedigree and individual performance records are helpful in getting an initial understanding of a beef animal’s genetics. But genotyping takes their EPD estimates to a more accurate level, helping breeders know what trait levels they are dealing with and enabling better selection decisions.
