Time for Change
Change is inevitable, especially in science-based industries that strive for progress, such as the dairy industry. This January, one change affected all genetic evaluations and all breeds. This change was a genetic base change.
What is a genetic base?
Genetic evaluations of dairy cattle (such as +1500 PTA Milk or -0.02% Fat) are expressed relative to a base population. The genetic level of the base population is known as the genetic base.
Why have a base change?
A base change serves two basic purposes: 1) It measures the genetic improvement of the dairy population by trait, and 2) it adjusts the sire evaluations to a more current genetic level in the dairy population for each breed. In other words, the genetic base change subtracts accumulated genetic gain that occurred since the previous base change so all animals are compared with a more recent cow population.
How often does a base change occur?
In the United States, the evaluation system is updated to a new genetic base every five years.
What is the base population for the new genetic base?
The base population for the January 2010 base change is heifers born in 2005. This means the basis is the production from those animals in 2007 and later. (The previous genetic base was established from heifers born in 2000.)
Table 1. Genetic gain by breed between 2000 and 2005.
--------------------Genetic Progress-------------------- | ||||||
| Trait | Holstein | Jersey | Brown | Guernsey | Ayrshire | Milking |
| Lifetime Net Merit (Dollars) | 132 | 119 | 60 | 50 | 37 | 71 |
| Protein (Pounds) | 14 | 12 | 10 | 6 | 3 | 6 |
| Fat (Pounds) | 15 | 17 | 10 | 12 | 3 | 8 |
| Milk (Pounds) | 417 | 323 | 267 | 231 | 53 | 199 |
| Productive Life (Months) | 0.6 | 0.8 | 0.3 | 0.1 | 0.3 | 0.8 |
| Somatic Cell Score | -0.01 | 0.00 | 0.01 | 0.02 | -0.02 | 0.01 |
| Daughter Pregnancy Rate (%) | 0.0 | -0.1 | -0.5 | -0.4 | 0.1 | -0.1 |
| Udder Composite | 0.85 | 0.401 | 0.25 | 0.30 | 0.35 | 0.25 |
| Foot & Leg Composite | 0.65 | 0.20 | 0.10 | 0.30 | 0.15 | 0.15 |
| PTA Type | 0.87 | 0.62 | 0.30 | 0.54 | 0.25 | 0.00 |
What amount of genetic improvement occurred between the previous genetic base and the new genetic base?
The table, above, indicates the accumulated genetic gain by breed that occurred between the animals born in 2000 and the animals born in 2005. The genetic gains are published by the United States Department of Agriculture. While all evaluated traits are adjusted, the more significant traits are shown in the table.
The figures within the table are evidence the traits within the Lifetime Net Merit (LNM) formula have had significant genetic influence. Those traits of Fat, Protein, Productive Life, Daughter Pregnancy Rate (DPR) and Udder Composite are the traits that have made substantial improvement. This is much in-line with what dairies have asked for: high components cows that have longer productive lives.
How does the base change affect sire evaluations?
The genetic gain for each trait (as shown in the table) is subtracted from each bull's August 2009 evaluation for that trait. For instance, in August 1HO08784 FREDDIE's evaluation for PTA Milk was +1549. With the base change, you would expect his January evaluation for Milk to be about +1132 (1549 - 417 = 1132).
While the genetic gain for individual traits can simply be subtracted from a sire's proof, indexes or composites are treated differently. This is because indexes include various percentages of several traits, and each trait exhibits differing levels of genetic gain.
All bulls industry-wide were impacted by the base change. However, that fact may not be easily evident. After the base change was accounted for, the additional genomic or milking daughter data for a sire also impacted his evaluation. In addition, the LNM index and TPITMformula were updated with this sire summary.
Why is there limited or no change to the base in DPR with the emphasis put on it today?
DPR is a relatively new trait, first published in 2003. Since the base population for the base change is heifers born in 2005, one would not expect large genetic gains in the short time period between 2003 and 2005. However, it is important to note that previous to its introduction DPR was a more negative figure in each base change as milk yield increased. The recent move from a negative to a break-even trait was probably in part due to selection for Productive Life. The emphasis Genex has placed on DPR when procuring sires and the emphasis by dairy producers to utilize these bulls will force faster genetic improvement in the future.
How will genomics affect base changes in the future?
Genomics will have a significant affect on the 2015 base change - although not to the degree one might expect. The basis for the 2015 base change will be cows born in 2010. Since genomic sires were first introduced industry wide in early 2009, only a portion of heifers born in 2010 will have significant influence from genomics. The affect of genomics under the current system, with five years between base changes, will be better expressed in 2020. The genomic influence will show in the heifers born in 2015. These animals will compose the base population for the 2020 base change.
1The base adjustment for the Jersey udder composite is a summation of the values for udder traits used in calculating LNM and is not synonymous with JUITM.
posted January 2010
