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Using somatic cell score evaluations for management decisions

B G Cassell1

  • 1Virginia Polytechnic Institute, Blacksburg 24061-0315.

Journal of Dairy Science
|July 1, 1994
PubMed
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Genetic evaluations for somatic cell score (SCC) help manage mastitis. While selection for lower SCC is not yet economically justified, improved breeding indexes can reduce mastitis incidence without significantly impacting milk yield.

Area of Science:

  • Animal Genetics
  • Dairy Science
  • Mastitis Research

Background:

  • Genetic selection for milk yield can inadvertently increase somatic cell score (SCC), a key indicator of udder infection.
  • Current progeny testing methods yield lower reliability for SCC evaluations compared to milk yield due to lower heritability.
  • Genetic correlations for SCC between lactations are weaker than for milk yield, leading to more dynamic sire evaluations over time.

Purpose of the Study:

  • To evaluate the impact of genetic evaluations for mean somatic cell scores on mastitis incidence and milk production.
  • To assess the economic justification of selecting for reduced somatic cell scores.
  • To determine the potential benefits of using properly constructed breeding indexes for mastitis control.

Main Methods:

Related Experiment Videos

  • Analysis of genetic evaluations for somatic cell scores in dairy populations.
  • Comparison of sire evaluation changes over time for SCC versus milk yield.
  • Modeling the effects of genetic selection for SCC on mastitis incidence and milk yield progress.

Main Results:

  • Absence of genotype-environment interaction for SCC suggests consistent bull selection across different herd SCC levels.
  • Holstein bulls with the highest SCC evaluations show a 50% increase in geometric mean SCC and 11% higher clinical mastitis incidence.
  • Direct selection to reduce SCC is not currently economically justified, but integrated indexes show promise.

Conclusions:

  • Properly constructed breeding indexes can decrease projected mastitis incidence by 20-25% with only a 2% reduction in genetic gain for milk yield.
  • The most significant impact on mastitis reduction through genetic evaluations may come from selecting sires for progeny testing.
  • Further research into economically viable genetic strategies for mastitis control in dairy cattle is warranted.