Genotype by environment interaction (G * E) for lactation average somatic cell count (LSCC) and clinical mastitis incidence (CM) in environments defined by protein production, LSCC, CM and herd size was studied for >200 000 first-parity Swedish Holstein cows using a random regression model. The clearest evidence of G * E was detected for LSCC in LSCC environments as significant genetic variation in slope of predicted reaction norms and low genetic correlations between average and deviating environments, indicating re-ranking of sires. G * E was also found for CM in LSCC environments, for LSCC in CM environments and for both traits in protein production environments. In practice, the detected G * E for LSCC in LSCC environments could affect the selection of bulls in the progeny testing program.

E. Carlen, K. Jansson, E. Strandberg

Proceedings of the World Congress on Genetics Applied to Livestock Production, Volume , , 25.10, 2006
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