Daughter Data Shows Stability of Genomic-Proven Bulls
By Angie Coburn, Dairy Procurement Manager
If you didn't hear the word "genomics" in 2009, you probably didn't work in the dairy industry. Early adopters quickly embraced the opportunity to use genomic-proven bulls at higher genetic levels. Others took a more cautious approach waiting to see how things looked after time had passed.
The burning question in everyone's mind is, "How do genomic proofs compare with progeny proofs?" To answer this question, let's look at bulls based on their initial genomic PTA without any milking daughters and compare that to their current progeny proof. The table shows the average change for several trait PTAs for two groups of bulls selected by birth year. The graph illustrates the distribution of bulls by their average change.
Table 1. Comparison of genomic-proven proof to progeny-proven proof for Holstein bulls by birth year
| ---------------------------Average Change in Trait PTA-------------------------- | |||||||
Birth Year | Number of Bulls | LNM$ | PTA Milk | Prod. Life | # Dau. (Production) | PTA Type | # Dau. (Type) |
2002-2003 | 830 | -54 | -112 | -0.3 | 138 | -0.06 | 87 |
2004-2005 | 1025 | -94 | -185 | -0.3 | 91 | -0.05 | 54 |
Note: Adjustments have been made to PTAs for base change and method of calculation
Bulls born in 2002 and 2003 were the first bulls to have a genomic proof independent of milking daughters and is therefore the most complete data set to conduct this type of analysis. Bulls born in 2004 and 2005 have daughters milking in their first lactation and while they are still adding daughters to their proofs, similar trends are present. USDA-AIPL continues to refine the methods used to incorporate DNA information into genetic PTAs making them even more stable and accurate.
Several conclusions can be made:
The average change is quite stable. It's unreasonable to expect every bull to have zero change, but the average change should be quite close to it.
A slight negative change is to be expected. While genomics helps to minimize the effect of preferential treatment on bull dams, it cannot totally remove it. So long as there is bias present in contract cow data, a negative average change is likely.
The vast majority of bulls change very little. Nearly 90 percent of the bulls fall within the acceptable range of one standard deviation. It is appropriate to expect bulls to change +$125 for Lifetime Net Merit. Using the average change as the mid-point, the bulls have a very normal distribution with half being lower than average and half being above average.
It is often stated that progeny PTAs exceed genomic PTAs for reliability, thus it's important to still have progeny. Repeated validation testing has been done by a number of research geneticists and A.I. industry representatives, and the results are consistent among all studies. Have confidence in genomic-proven bulls and put them to use. The same rules apply as before. Don't put all your eggs in one basket and use a group of genomic-proven bulls instead of just selecting one or two. Use the bulls with the highest genetic levels. Let the PTA of the bull determine if you use him or not and let the reliability determine amount of use.
Genomics is here to stay and has yielded very positive benefits for dairy producers. For further reading, check out Capture the Most Genetic Progress from Genomic-Proven Bulls.
