Genetic improvement of mastitis resistance: validation of somatic cell score and clinical mastitis as selection criteria.
Mean daughter deviations for clinical mastitis among second-crop daughters were regressed on predicted transmitting abilities for clinical mastitis and lactation mean somatic cell score in first-crop daughters to validate the predictive ability of these traits as selection criteria for reduced incidence of clinical mastitis. A total of 321 sires had 684,897 second-crop daughters, while predicted transmitting abilities were calculated for 2159 sires, based on 495,681 records of first-crop daughters. Predictive ability, as a measure of efficiency of selection, was 23 to 43% higher for clinical mastitis than for lactation mean somatic cell score. Compared to single-trait selection, predictive ability improved 8 to 13% from utilizing information on both traits. The relative weight that should be assigned to standardized predicted transmitting abilities from univariate genetic analyses were 60 to 67% for clinical mastitis and 33 to 40% for lactation mean somatic cell score. No significant nonlinear genetic relationship between the two traits was found.
Odegård
J
J
Department of Animal Science, Agricultural University of Norway, P.O. Box 5025, N-1432 As, Norway. jorgen.odegard@ihf.nlh.no
Klemetsdal
G
G
Heringstad
B
B
D000704:Analysis of Variance; D000818:Animals; D002417:Cattle; D002452:Cell Count; D005260:Female; D007113:Immunity, Innate / Q000235:genetics*; D007774:Lactation / Q000235:genetics*; D008414:Mastitis, Bovine / Q000235:genetics*; D008892:Milk / Q000166:cytology*; D012044:Regression Analysis; D012641:Selection, Genetic