Journal of Dairy Science, Vol 75, Issue 4 1127-1137, Copyright
© 1992 by American Dairy Science Association
Genetic evaluation of Holstein bulls for somatic cells in milk of
daughters
P. J. Boettcher, L. B. Hansen, P. M. VanRaden and C. A. Ernst
Department of Animal Science, University of
Minnesota, St. Paul 55108.
Lactational means of somatic cell score from sample days of primiparous
DHI cows were analyzed to compare dairy records processing centers
for data properties, to examine effects of age at calving and month
of calving on somatic cell score, and to calculate preliminary PTA of
sires for somatic cell scores. Five processing centers contributed
data but differed substantially with respect to availability of
records in progress, DIM on last sample day, and length of time that
data were submitted. Highest lactational means of somatic cell score
tended to be in short lactations for young cows but in long
lactations for older cows. Regions of the country differed
substantially for effect of month of calving on lactational means of
somatic cell score, but lactational means of somatic cell scores
increased with age at calving for all dairy records processing
centers. Standardized yields of milk, fat, and protein were included
as multiple traits with somatic cell score for analysis. Heritability
of somatic cell score was .08 to .16 for individual processing
centers and .10 across processing centers. Phenotypic correlations of
somatic cell score with yield traits were negative, but genetic
correlations were positive. Selection for decreased somatic cell
score on a national basis should be possible and would seem advisable
to decrease mastitis infections. Response may be slow, however,
because of antagonistic genetic relationships with the yield traits,
which have great economic importance.
