Expect genetic changes

Just as a baseball player adjusts and fine tunes his swing between games, dairy geneticists continually look for ways to tweak and improve the genetic information available to producers between the quarterly sire summaries.

This August, you will find new formulas for the Holstein Association's Type Production Index (TPI) and a newly-designed body size composite to replace the body form composite. In the data published by the USDA's Animal Improvement Programs Laboratory, you'll see new calculations for the Net Merit, Fluid Merit and Cheese Merit indexes. And, all traits will be calculated with a new genetic base.

Although genetic progress doesn't move quite as fast as a Sammy Sosa home run ball, it does continue to increase the quantity and components of milk, as well as change the shape of today's dairy cow. You need to be aware of these changes as you make semen purchases in the upcoming months. Some numbers will look different — be sure you understand why.

Here's what you need to know:

Updating the genetic base
When you look at data on a sire, remember you're looking at a comparison. The numbers reflect how well a bull's daughters produce and score in type evaluations when compared to a group of average cows. With the August 2000 release of information, the average group shifts from cows born in 1990 to cows born in 1995.

Because genetics help improve production in the nation's cow herd every year, the production of the "average" cows in the comparison increases with each base change. USDA-AIPL geneticists estimate that the average cow born in 1995 produced 1,336 more pounds of milk, and 40 pounds more protein and milkfat, than the average cow born in 1990. This change will cause the sires" Predicted Transmitting Abilities (PTAs) to drop by 668 pounds for milk and 20 pounds for both milkfat and protein. The sires" PTAs drop by half the value, as they contributed half of the genetics to the cows. While it is a negative change in the PTA, it reflects positive genetic progress.

For example, in the May 2000 sire summary, the Holstein bull 11H4623 Hershel, had a PTA milk value of 3,597. That means his daughters, on average, produced 3,597 more pounds of milk than the average Holstein cow born in 1990. However, if the base had been updated for the May evaluations, Hershel's PTA milk would have been just 2,929.

When evaluating the base change's effect on type traits, remember that the scale used in these comparisons ranges from +3 to -3, with zero representing the breed's average. So, in the May 2000 sire summaries, the bull 29H8557 Brett had an udder depth score of 0.4. With the base change, the average cow improved in udder depth by 0.4, thus Brett's score would have been zero in May if the base change had taken effect.

When looking at August sire summary data, expect lower values for PTA milk, protein and milkfat, as well as shifts in type traits. And, remember that all bulls move by the same amount with the base change. "The most important thing is to avoid comparing data calculated from the old base with the new base," says Duane Norman, geneticist at USDA-AIPL.

Changes to indexes
In addition to the base change, the formulas used to calculate several indexes have changed. Each one is listed below:

  • TPI Index. The TPI index will now include PTA productive life and PTA somatic cell score information. The previous formula included PTA protein, PTA milkfat, PTA type and 0.65 udder composite and 0.35 feet and legs score, and weighted them according to a 3:1:1:1 ratio. Now, the calculation will be 4:2:1 for production, type and health. (Within the production component, the measure will be 5 parts PTA protein and 2 parts PTA milkfat. Within the type component, it will be 1 part PTA type, 0.65 udder composite and 0.35 feet and legs composite. Within the health component, it will be 0.9 PTA productive life and 0.1 PTA somatic cell score.)

    According to Tom Lawlor, director of research and development for the Holstein Association, the new TPI calculation has a high correlation — 0.989 — to the old formula. That means a bull's ranking under the new formula will be very similar to the old.

    Lawlor says Holstein breeders suggested the changes. "Producers were anticipating the changes in federal milk marketing orders, and wanted to get a higher weight on milkfat," he says. Producers also wanted to include information on health characteristics, which led to the inclusion of PTA productive life and somatic cell scores.

  • Body size composite. The Holstein Association also will be changing its body form composite to a body size composite. The old body form calculation emphasized the type traits of stature, body depth, rump angle and thurl width, with a similar weight for each. For the new calculation, rump angle has been removed and body strength has been added. The ratio is now 10:5:3:2 for stature, body strength, body depth and thurl width.

    "The old body form composite told you more about the shape of the cow," says Lawlor. "The new body size composite will tell you more about the size of the cow."

    The change in the body size composite follows a change in thinking about the value of tall cows. Research at the University of Minnesota suggests that large, tall cows are not the most cost-effective milk producers. The new ranking gives producers a clearer picture of the size being transmitted.

    On the -3 to +3 scale used for type traits, a body size composite of +3 would indicate larger body size, with a -3 indicating a smaller body size. If you consider 1,500 pounds as average (or zero on the scale) for a Holstein cow, then each point on the scale represents about 24 pounds of mature body weight.

    While most producers do not select directly on size, Les Hansen, dairy geneticist at the University of Minnesota, says the industry has indirectly selected for the trait in the past when selecting for udder depth. In other words, bulls that transmit to their daughters udders held higher above the hocks than the average cow also tend to transmit taller stature to their daughters.

    "Our research indicates that, on a genetic basis, larger Holstein cows have reduced productive life compared to smaller Holstein cows. Therefore, it is probably economically important that we halt the continued selection for larger and larger Holstein cows," says Hansen.

  • Net, Fluid and Cheese Merit indexes. The three Merit indexes — designed to incorporate genetic information for production, longevity and somatic cell score with milk prices and feed cost — will undergo several changes.

    First, the indexes will now include type traits to help evaluate the longevity of sires" daughters, as well as the likelihood of them contracting mastitis. Currently, the Merit indexes use PTA productive life to evaluate longevity and PTA somatic cell score to evaluate mastitis. Both measure these traits "after the fact," or in terms of how many months a bull's daughters last in herds and what their somatic cell counts were.

    By including type traits, geneticists can incorporate some of the characteristics thought to result in culling and mastitis, such as poor udders and feet and legs at the time the animal freshens. This becomes important when evaluating bulls with just "first-crop" or first-lactation daughters. These daughters may not have been around long enough to be culled or contract mastitis, but will still have type characteristics that might predispose them to problems.

    The second change to the Merit indexes is the inclusion of a body size composite. However, it will carry a negative weight, says Gary Rogers, dairy geneticist at Penn State University. "The level of negative weight will not necessarily lead to smaller cows," says Rogers. However, it will help stop the gradual increase in cow size that has occurred over time as producers emphasized udder traits.

    The final change in the Merit indexes is that the dollars and cents portion of the equation will now be calculated as a lifetime profitability. Previously, the three indexes were calculated as the profit for one lactation. Geneticists say the average U.S. cow has 3.3 lactations, so an average of three lactations will be used in the formula. Therefore, even with the base change, expect the NM, FM and CM values to increase.
 
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