Genetic parameters were estimated for somatic cell score (SCS), using a random regression test-day model, including random regressions on days in milk (DIM), bulk milk somatic cell count (BMSCC), and the interaction between DIM and BMSCC. The random regressions on BMSCC and the interaction between DIM and BMSCC were included to account for genotype by environment interaction (G * E). In herds with low BMSCC genetic variances increased with increasing DIM, while in herds with high BMSCC, genetic variances decreased with increasing DIM. Estimated heritabilities changed considerably across DIM in herds with low BMSCC, but did not change across DIM in herds with high BMSCC. Genetic correlations between SCS expressed in herds with low and high BMSCC values were as low as 0.72 early in lactation.

Mario PL Calus, M. H Pool, Roel F Veerkamp

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume , , 25.06, 2006
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