What You Can't See - How Genomics Can Break the Tie

 We have all heard the saying “You can’t judge a book by its cover”, but it is true that the cover is what initially draws a person to pick up the book in the first place. The same is true with selecting and breeding cattle. What the animal looks like matters. However, what the saying really means is it’s what is inside the book, or in this case underneath the animal’s hide, that adds the most value.

The importance of phenotypic selection in cattle is non-negotiable. But, once someone has made that initial gate cut, genomics can help in marketing the value of sale bulls and heifers with increased confidence.

Cattlemen and women do their best to select elite bulls to mate their cows to. Unfortunately, basic biology reminds us that variability exists even within the best mating plans. But exactly how much variability? Well, while discussed at length in the extension article The Random Shuffle of Genes: Putting the E in EPD, basic math tells us that within a single full sibling mating, there are over one quintillion possible combinations of chromosomal inheritance (DNA passed from sire/dam to offspring). Therefore, producers could be standing in a pen looking at two prospective full sibling sale bulls that phenotypically look the same, but whose genetic merit could be different. But differentiating those cattle on sale day goes one step beyond just looks and Expected Progeny Differences (EPDs).

Table 1. Expected Progeny Differences for Calving Ease Direct, Birthweight, and Ribeye Area for a sire and dam, along with 6 full sibling progeny resulting from said mating¹

Animal	CED	BW	REA	GE-EPDs
Sire	+2.3	+2.9	+0.67	Yes
Dam	-4.7	+5.5	+0.35	Yes
Heifer 1	-3.9	+5.8	+0.46	Yes
Heifer 2	-9.2	+8.1	+0.55	Yes
Heifer 3	-5.7	+7.4	+0.60	Yes
Bull 1	-1.3	+4.2	+0.51	No
Bull 2	-1.3	+4.2	+0.51	No
Bull 3	-1.3	+4.2	+0.51	No
1Data reported are real EPDs and GE-EPDs pulled from a breed association.

 Using Table 1 as an example, data has been captured on six embryo transfer (ET) calves (3 bulls and 3 heifers) born from the same sire and dam mating. Phenotype based EPDs are estimated using the pedigree, phenotype, and progeny information on an animal. Yet when full siblings are born, they share the same pedigree, and therefore the same phenotypic information stored within the genetic evaluation. This means that until their own phenotype or progeny information is reported, their EPDs for all traits are simply the average of their parents. This is illustrated in Table 1 when looking at the bull progeny who all appear to have the same genetic merit for calving ease direct (CED), birth weight (BW), and rib eye area (REA).  However, unless identical twins, no two siblings look, act, or perform the same.

So how does one differentiate or capture the genetic difference between those calves? Taking a DNA sample on an animal early in its life and reporting that to the evaluation will immediately inform the prediction which pieces of DNA each relative inherited from the members of their pedigree (i.e. which 50% they received from their sire and dam, respectively) and therefore differentiate cattle early in their lives. This differentiation can be seen in the heifer progeny listed in Table 1 that have a genomic profile on file.

The benefit of adding the genomic test on any registered animal, related or not, is still the same. It gives the evaluation a much better picture of the DNA inherited from an animal’s sire and dam, and therefore increases the accuracy of the prediction. Most importantly, it better defines the genetic potential of an animal and helps the producer or buyer align that individual to their specific breeding objectives and goals.