It is time to update the service sire selection goals for your herd. As a result of the genetic base update, the February 2005 predicted transmitting abilities (PTAs) for most economically important traits are significantly lower. The approximate changes in Net Merit (NM$) were -$76 for Ayrshires; -$146 for Brown Swiss; -$100 for Guernseys; -$155 for Holsteins; and -$128 for Jerseys. The significant drop in NM$ was evident when you monitored the genetic merit of service sires in your herd following the February 2005 evaluations.

The base for genetic evaluations was changed in February 2005 to account for the genetic improvement from 1995 to 2000. The base population for each dairy breed is now cows born in 2000. (My article in the January 2005 issue of the Michigan Dairy Review highlights the genetic update process and the estimated genetic improvement for the traits in NM$.)

Net Merit

NM$ is a selection index used by dairy producers to make sire selection decisions. It is defined as the expected lifetime profit expressed relative to the base population for the breed.

NM$ combines genetic evaluations for production, health, and fitness traits. The traits are weighted based on known or estimated economic values. Relative emphasis on the traits for Holsteins is 55% production traits and 45% health and fitness traits. The relative emphasis for the other breeds is 57% production and 43% health and fitness.

Genetic evaluations are used to rank animals based on genetic merit. NM$ or other PTAs are more meaningful when you know where the specific value ranks among the animals from which you are selecting.

USDA’s Animal Improvement Programs Laboratory (USDA-AIPL) provides percentile rankings for NM$ to help you determine the relative superiority of service sires. For example, if a bull’s percentile rank is 75, then his NM$ is higher than 75% of the active AI bulls. To maximize genetic improvement, it is recommended that the service sires in yourherd average at or above the 80th percentile. Table 1 lists the NM$ levels of top percentiles for AI sires.

Monitoring Herd Trends

Herd owners and managers using Dairy Herd Improvement (DHI) records can easily monitor NM$ of service sires used to breed the herd. The DHI Template kit is a new herd monitoring tool developed by the MSU Extension Dairy Team and recently provided by DHI service affiliates serving Michigan DHI herds. Using the DHI templates, you can quickly locate the “Percentile Rank of Proven AI Sires” and “% Cows Bred to AI Sires” reported on the DHI-202 Herd Summary report. These values are two key indicators of genetic meritof future herd replacements.

You might consider monitoring “Percentile Rank of Proven AI Sires” and “% Cows Bred to AI Sires” quarterly when new genetic evaluations are released (February, May, August and November). At that time you can also determine if any bulls represented in the herd’s semen inventory no longer meet your sire selection criteria.

Summary

Choosing genetically superior service sires is an important investment that you make in your herd. Use the tools available to ensure that your future replacement heifers have the genetic potential to be profitable cows.



April 2005