Holstein USA Announces Changes to November Top 100 TPI list
By Tom Lawlor
Holstein USA has announced changes to the TPI formula and reliability requirements for inclusion in the Top 100 listing to be implemented with the November sire summary. The changes are primarily aimed at increasing the impact of SCS and type on the TPI score as well as a modification of the protein to fat ratio that sees increased emphasis placed on fat relative to protein yield. Reliability requirements for inclusion in the Top 100 listing will increase for both type and production and in addition, a reliability figure will begin to be listed beside the Productive Life rating. Here is a detailed explanation on the changes and expected impact on rankings.
1. Formula change: Increased emphasis will be placed upon better health (increased negative weighting on SCS) and conformation (slight increases to weighting on both PTAT and Udder Composite). In addition, the ratio of Protein to Fat will be modified to reflect current multiple component pricing (decreases the weighting on protein and increases it on fat).
2. Reliability Requirement: The reliability requirement for inclusion will be raised from 75% for Production and 70% for Type to 80% for Production and 75% for Type. This will result in a list of bulls with more stability in their proofs.
3. Productive Life Reliability: The reliability for Productive Life will be printed as part of the top 100 format. This value will help breeders to more easily see the amount of daughter information in the Productive Life evaluations.
Traditionally, TPI has always had a constant, a mean and a variance. Because of the change in expression of the formula the two factors that are used for multiplication and addition change dramatically. Instead of multiplying by 45 this becomes 3.3 and the number to add is now 1241 instead of 956. The average cow in the base population, those born in 1995, now has a TPI of 849 with a standard deviation of 192. These numbers are the same as before.
Impact on Bulls
In August 2002 there were 732 bulls in the available bull population that had both production and type evaluations based on daughter performance. The average TPI of these bulls was 1347. Using TPI_n these bulls will have an average TPI of 1348. This shows that on average bulls will only change minimally due to the new TPI formula. Keep in mind however, that some bulls might change by as much as 83 points (downward) to 62 points (upward). Table 1 shows the average evaluations for the 47 bulls that went up by at least 30 points and the 35 bulls that went down by at least the same amount.
This Table shows that the change in the formula had the intended results. Bulls that go up are typier, have better health, and tend to have higher fat than protein evaluations than those that go down.
Impact on Top 100 TPI
The impact of the changes on the Top 100 TPI listing is two-fold. First there is the effect of the new formula and secondly there is the effect of the change in the reliability requirements. To assess the impact of these changes three different Top 100 TPI lists were created: 1. Top 100 TPI as in August 2002. 2. Top 100 TPI using the new TPI formula but using the old reliabilities. 3. Top 100 TPI using the new TPI formula, but using the new reliability requirements. Average evaluations for each of these Top 100 lists are in Table 2.
When comparing both TPI formulae with the same reliability restriction it shows that the new weights had the intended effect on this selected group of bulls. Under the new formula the bulls in the Top 100 have better SCS evaluations without giving up PL. They also have slightly better type evaluations than under the old formula. As far as production is concerned they have the same amount of fat and slightly lower protein.
When comparing the new TPI for the different reliability requirements, it is clear that the stricter requirements mean that one has to go further down the TPI list to find bulls that qualify. This comes at a cost to the average PL, and type. However, SCS and the production evaluations remain constant.
An example of the Top 10 TPI bulls in August 2002 is given in Table 3. This table shows that for most of these bulls the TPI tends to go up slightly. Bulls that change the most have low (Mtoto and Ozzie) or high (Garter) SCS. Some switching of position will occur among this group of bulls but no major re-rankings will occur because of the new formula. Bulls that have a PTAF that is much higher than their PTAP also see an increase in their TPI (Stormy and Magna). Under the new publication rules Beaver and Stormy would not have qualified for the Top 100 TPI.
The new TPI formula puts more emphasis on the type and health component of the TPI. Comparisons of groups of bulls show that the change has its intended effect. The new requirement for the reliability to qualify in the Top 100 TPI comes at a cost for the average genetic level of this group, however, the additional reliability should result in more stable evaluations in this group of bulls.