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The genetic correlation between milk yield and fat percentage for 5,458 Holstein daughters and their dams was --0.38 0.06, and for 1,825 Guernseys, --0.57 0.10. The genetic variance in fat percentage for Holsteins was about one-half that for Guernseys, but for milk production it was larger for Holsteins than for Guernseys. There was no consistent trend in the negative genetic correlation between milk production and fat percentage for either breed, when fat production increased from 300 to 480 lb.
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Farthing et al. (1957) studied this question.
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