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Virginia Cooperative Extension - Knowledge for the CommonWealth

Include somatic cell score in breeding programs.

Dairy Pipeline: April 2004

Bennet Cassell
Extension Dairy Scientist,
Genetics and Management

Dairy producers have emphasized production and type in breeding programs for many years, but genetic evaluations for other important traits are now available including longevity, fertility, dystocia and somatic cell score or SCS. These "new" traits are gaining attention because they reduce costs of production, and they don't necessarily flood an already saturated milk market with more product in the process. SCS is an indicator trait for clinical mastitis, the most costly disease of dairy cattle. We can use selection programs to develop cows genetically disposed to fewer mastitis infections. Daughters of some bulls have lower SCS than daughters of other bulls because their bodies respond to and eliminate infection quickly and/or because their mammary systems are less prone to infection in the first place. Genetic evaluations for SCS are a little different from most other traits. Lower numbers are better - an SCS proof of 2.80 is better than a proof of 3.20. The average Holstein bull in active AI service has a SCS of 3.10. Bulls with SCS evaluations below 2.94 are pretty special, as they have lower SCS proofs than 5 of every 6 active AI Holsteins bulls available. Average proofs for Jersey bulls are higher than for Holsteins, averaging 3.28. Jersey bulls with SCS evaluations below 3.13 have better SCS proofs than 5 of every 6 active AI Jersey bulls available. SCS is included in the selection index Net Merit, receiving 9% of total emphasis on all traits. It is one of the most important non-production traits in Net Merit, and, if anything, it doesn't get as much weight yet as it will likely receive in the future. Genetically lower SCS is valuable. First of all, it is permanent, and benefits the recipient animal throughout her life. It can help a herd qualify for quality milk premiums. Lower SCS leads to reduced mastitis treatment costs, lower risks of contaminated milk, less discarded milk, less cross-cow contamination, and less labor to manage cows with mastitis. But the biggest economic value would be higher yield from cows with low SCS - between one and two lbs. of milk a day for each reduction of 1 unit of SCS. Genetic improvement in SCS deserves more attention. Check out the AI bulls on your mating list to see if they are helping you to breed a healthier herd.

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