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One of the most common and costly diseases impacting dairy producers around the world is Mastitis, or infection of the udder. The economic impact of mastitis extends beyond treatment costs to losses in milk production, delayed reproduction and increased cull rates. Proper milking procedures, cleanliness of housing, cow comfort AND genetics all factor into reducing the prevalence of mastitis.
Somatic Cell Score
Over the past 30 years, Somatic Cell Score (SCS) in Holsteins has declined to a point lower than most could have imagined possible. When the genetic evaluation for SCS was first implemented, few would have anticipated that SCS would ever be below the level of 3.0, so 3.0, which equates to 100,000 SCC, was used as the “zero” for Predicted Transmitting Ability (PTA) for SCS in genetic evaluations. It is for this reason that the PTA value for the base population is reset to 3.0 PTA SCS with each base change.
To adjust PTA SCS values to expected SCS for a bull’s mature daughters, subtract 3.0 from PTA SCS and add the resulting value to the Base Population Average. The current Holstein base population, born in 2015, averages 2.31 SCS. Therefore, the daughters of a Holstein bull who is 2.95 SCS would be expected to average 2.26 SCS in mature lactation.
Example: Average Mature Daughter of 2.95 PTA SCS Holstein Sire
2.31 + (2.95 – 3.0) = 2.26 SCS, which is less than 50,000 SCC
What About Mastitis Incidence?
Economic losses associated with clinical mastitis are estimated to range between $128 and $444 per case, with the costs extending well beyond the immediate treatment of the disease.
While we have seen a dramatic decline in SCS in Holsteins, we recognize that SCS does not directly correlate with mastitis incidence and that improved resistance to mastitis is required. It was for this reason that Zoetis and CDCB developed genetic evaluations for Mastitis Resistance.
Economic Impact
31% Milk Yield Losses
24% Veterinarian and Drugs
23% Premature Culling
18% Discarded Milk
4% Excess Labor
Real Life Example
In herds with accurate data for SCC and mastitis, the relationship between genetics and disease incidence for these traits is clear. The quartile analysis below shows the mastitis incidence in a 3,500-cow dairy in the USA. Genomic SCS values continue to be an indicator of mastitis resistance. However, as evidenced in this herd, evaluations directly measuring mastitis resistance (CDCB_MAST) more clearly expresses the genetic influence on mastitis resistance. In 2nd lactation cows, we see a 24.6% difference between highest (most resistant) and lowest (least resistant) CDCB_MAST groups, compared to only 7.1% difference with G_SCS.
Conclusion
Combining best management practices with genetic resistance to mastitis is critical in maximizing animal welfare, milk quality and farm profitability. To maximize genetic resistance to mastitis, consider using bulls identified with the MastitisResistantPro designation. MastitisResistantPRO uses a combination of CDCB Mastitis Resistance, CDCB Somatic Cell Score (SCS) and Zoetis Mastitis Resistance to identify sires which excel in multiple indicators of mastitis resistance and are more likely to deliver genetic improvement for mastitis resistance.