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The 85,271 observations of test-day somatic cell count were on 17,477 Holstein cows with identified sires in 664 herds on the Quebec Dairy Herd Analysis Service during 1977. Somatic cell counts were transformed to a log (natural) scale and corrected for effects of month of test, age of sample at analysis, stage of lactation, season of calving, and age of cow. Analysis was within lactation and age. Heritability of test-day somatic cell count ranged from .05 for ~ 2 yr olds to 10 for mature (/> 6 yr) cows, and averaged .08 over all ages. Phenotypic correIations between somatic cell count and milk, fat, and protein yield, and fat and protein percent averaged -. 13, -. 13, -. 11, -. 02, and .09 and increased in absolute size with advancing age of cow. Respective average genetic correlations were. 14, .08, .18, --.08, and .04.
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Kennedy et al. (1982) studied this question.
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