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Abstract
A program has started in Sweden to screen the udder health status of individual cows by bucket somatic cell counting. A study was undertaken to investigate the genetic variation in test-day somatic cell counts (SCC) in milk sampled at monthly intervals. The material included data from two breeds and totalled 87760 observations. The SCC were transformed to a log scale with base ten (LSCC). The heritability estimates were generally low, ranging from 0.02 to 0.15. Heritabilities increased with lactation number up to the third, while lactation no ≧4 was rater lower. Large breed differences in heritabilities were revealed in lactations 1 and ≧4, but virtually no differences were seen in lactations 2 and 3. Analyses on each lactation stage and on part-lactation gave erratic results for one breed, while the results for the other breed were more consistent, indicating higher heritability estimates in late lactation. The results indicate that a significant genetic change in LSCC can be obtained. Correct conclusions about the incorporation of LSCC in breeding activities cannot be drawn, however, without further research into genetic correlations with actual mastitis incidence and with production.
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