HealthMark™: A New Tool to Identify Health Trait Specialists

In today’s commercial dairy environments, health and fertility traits are becoming more and more important. Recent results of a dairy producer survey conducted by USDA's National Animal Health Monitoring Service indicate that the primary reasons cows are removed from herds are mastitis problems and reproductive problems. These two reasons account for 53.4 percent of all cows leaving the herd. The survey also shows that low production is less and less of a reason why cows leave the herd.

Dairy producers know that keeping cows healthy and in the herd is crucial to improving the bottom line. That is why we see more producers considering genetic values for Somatic Cell Score (SCS), Daughter Pregnancy Rate (DPR) and Productive Life (PL) in choosing their A.I. sires.

Somatic Cell Score

SCS genetic evaluations are computed based on the somatic cell count data that comes from routine monthly DHIA tests. SCS measurements provide an indicator of clinical and sub-clinical mastitis in bulls’ daughters. The correlation between SCS and clinical mastitis is between 60 and 70 percent.

Predicted transmitting abilities (PTA) for SCS generally range from 2.50 to 3.50. Higher values indicate bulls with daughters that tend to have higher somatic cell counts. Therefore, bulls with lower SCS PTA’s are preferred. SCS is a trait that is influenced more by management and less by genetics. For this reason, SCS PTA’s tend to have lower reliabilities than the customary production and type evaluations. New graduates will enter the lineup with reliabilities for SCS PTA at about 70 percent and these will remain pretty steady until the second-crop daughters arrive.

Daughter Pregnancy Rate

DPR genetic evaluations use breeding dates and freshening dates reported in DHI records to calculate the number of days open in each lactation for cows as an indicator of fertility. USDA uses this data to rank bulls based on how quickly their daughters breed back. By looking at days open, the DPR PTA’s take into account how quickly after calving cows come back into heat and also their conception rate when bred.

DPR values range from +3.0 to –3.0 with higher values preferred. They represent the percentage of eligible cows that become pregnant during each 21-day cycle. Each point of DPR corresponds to four days open. Higher values for DPR PTA are preferred.

The genetic control of fertility is notoriously low but with DPR we are able to gather several observations for each cow during her lifetime. Holstein sires will enter the marketing lineup with DPR reliability of 50-55 percent and then gradually climb to about 60 percent reliability over the next several proof runs.

Productive Life

PL genetic evaluations rank sires based on the longevity of their daughters. They use the calving dates and days in milk from lactation records gathered by DHIA to indicate how long cows remain in the herd. Each cow gets credited with the number of months she is lactating. The number of months she is dry are not counted.

PL PTA’s generally range from –7.0 to +7.0 and represent the number of months of additional lifetime that can be expected from a bull’s daughters. PL is influenced more by management than by genetics. It also is observed only once during an animal’s lifetime so there are fewer data points to use to predict an animal’s genetic merit. Reliability for PTA PL will start around 55 percent on new graduates and will gradually increase as productive life data comes in.

DNA Markers Can Help

One thing health and fertility traits have in common is that the genetic evaluations have low reliabilities until bulls reach their second-crop proofs. This makes sire selection decisions based on these traits difficult, especially since most sires being considered have first-crop proofs. This situation provides an excellent opportunity for DNA markers to improve the reliability of the available genetic information.

In October 2006, Merial introduced an updated IGENITY™ profile that includes new DNA markers for Productive Life and Dairy Form, both leading indicators of cow longevity. These markers were the result of a cooperative effort to validate potential genetic markers utilizing results of bulls progeny tested through the Program for Genetic Advancement™ (PGA™). The research identified several markers with a strong association with PL. The level of association and their relative impact on PL are listed in Table 1.

Bulls at Select Sires have been tested with these new genetic markers to provide extra information about their ability to transmit positive health traits. Comparing the PL PTA of the lineup sires that have high IGENITY PL scores to those with low scores provides additional evidence about the value of these PL markers. Table 2 indicates that lineup bulls with high IGENITY scores for PL, on average, transmit additional productive life to their daughters compared to sires with low IGENITY PL scores.

HealthMark – A Designation of Balanced Health and Fertility

To help dairy producers zero in on sires that transmit a balance of health and fertility traits, Select Sires has developed HealthMark. DNA marker results combined with genetic evaluation data for SCS, DPR and PL are used to identify HealthMark sires. This designation:
• Includes sires below (better than) breed average for PTA SCS.
• Includes sires above breed average for PTA DPR.
• Includes sires above breed average for PL based on PL performance information and their IGENITY PL score.

HealthMark Sires Stand the Test of Time

To illustrate the advantage of HealthMark sires, geneticists at Select Sires took the current criteria and applied it to the November 2002 national lineup. A comparison was made of their genetic evaluations at that time as well as their November 2006 evaluations, which had much higher reliability. Table 3 shows that the HealthMark designation effectively identifies outstanding health and fertility bulls even though their early genetic evaluations have low reliability. HealthMark is a unique and powerful tool to identify positive health trait bulls sooner than ever before, allowing producers to meet their breeding goals faster.

Choosing the Best HealthMark Sires for Your Herd

Recognizing that different operating environments call for different management and breeding strategies, we understand that you need to know more about HealthMark sires to find the ones that are right for your dairy. That’s why you’ll find details about Select’s HealthMark sires below. Your professional Select Mating Service™ (SMS™) evaluator and sales representative can work with you to health and fertility bulls even though their early genetic evaluations have low reliability. identify sires that will fit best in your program.

Backed by research and designed for use in the real world, HealthMark sires can put you a notch ahead in improving the health, fertility and profitability of your herd.