Results CMCR30. Directory UMM :Data Elmu:jurnal:L:Livestock Production Science:Vol67.Issue3.Jan2001:

268 B . Heringstad et al. Livestock Production Science 67 2001 265 –272 Table 2 Summary statistics of the data set CM120FIX used for the bivariate analysis of mastitis and culling and to examine the effect of accounting for culling as a fixed effect on variance component estimates of clinical mastitis. The sampling period was from 15 days before to 120 days after first calving, and the reference data set CM120 was defined as in Table 1 a CM120FIX CM120 Number of records 549,995 514,028 Number of sires 2043 2043 Number of herd3year classes 253,371 246,960 Mean number of daughters per sire 269 252 Mean number of records per herd3year 2.2 2.1 Mastitis frequency 14.9 15.9 Year of calving 1978–1995 1978–1995 a A total of 8.7 of the cows were culled before 120 days after first calving. 2 the first class and .32 months the last class, and the reasonably high h 5 0.033 and 0.034. It is also other classes are in single months, M is the fixed interesting to note the heritability of 0.016 when the j effect of the jth month of calving in 12 classes, HY sampling period ended at the day of first calving. k is the fixed effect of the kth herd by year class, S is Heritability estimates for CM120, CM150 and 1 the random effect of the cth sire, and E is a CM180, which correspond to the sampling periods ijklm random error term. used in Norway, Finland and Sweden, and Denmark, An additional fixed effect was included in the were 0.037, 0.039 and 0.040, respectively. Heritabili- univariate analysis of data set CM120FIX: C is the ty estimates transformed to the underlying scale were fixed effect of culling or not before 120 days after fairly constant, between 0.084 and 0.092. Estimates calving, in two classes 05not culled; 15culled. In of heritability from CMCR were slightly higher than the bivariate analysis of clinical mastitis and culling, from CM on both the observable and underlying and in the bivariate analyses of clinical mastitis from scale. different sampling periods, the same model as in the Table 3 shows the estimated variance components univariate analyses was assumed for both traits. for clinical mastitis CM and the mastitis variable An additive relationship matrix containing the where the trait is defined on the basis of clinical relationship between sires was included in the analy- mastitis and culling reason CMCR, for different ses. Variance components for random effects were length of the sampling period. Both the sire and the estimated with REML, using the program VCE4 residual variance components increase with increas- Neumaier and Groeneveld, 1998. Heritability esti- ing sampling period. Sire variance increases rela- mates were transformed from the observable 0 1 tively more than the residual variance, which results scale to the assumed underlying scale using the in higher heritabilities. The genetic variance was classical formula of Dempster and Lerner 1950. roughly twice as high for sampling periods up to 210 days CM210 and CMCR210 as for sampling periods ending 30 days after calving CM30 and

3. Results CMCR30.

The estimated genetic correlations between clini- Fig. 1 shows that heritability estimates on the cal mastitis measured in different time periods of the observable scale for both mastitis variables CM and first lactation are shown in Table 4. Genetic correla- CMCR increase with the length of the sampling tions between CM30, CM120, and CM210 were all period, and that the period from 15 days prior to high .0.94. The genetic correlations between calving to 210 days after calving resulted in the mastitis prior to calving CM0 and the other CM 2 highest heritability estimates h 5 0.042 and 0.043, variables were between 0.84 and 0.94. respectively. Heritability estimates for the sampling Tables 5 and 6 show the impact of cows culled period covering up to 30 days after first calving were before the end of the sampling period. For a sam- B . Heringstad et al. Livestock Production Science 67 2001 265 –272 269 Fig. 1. Heritability estimates of clinical mastitis CM and a mastitis variable where the trait is defined on the basis of clinical mastitis and culling reason CMCR for sampling periods from 15 days prior to first calving to date of calving 0 or to 30, 60, 90, 120, 150, 180 or 210 days after calving. Heritability estimates transformed to the assumed underlying scale CM-t and CMCR-t using the formula of Dempster and Lerner 1950 are also included. Table 3 2 Variance components and heritability h of clinical mastitis CM and a mastitis variable where the trait is defined on the basis of clinical mastitis and culling reason CMCR for sampling periods from 15 days prior to first calving to date of calving 0 or to 30, 60, 90, 120, 150, 180 or 210 days after calving Clinical mastitis CM Clinical mastitis and culling reason CMCR 2 2 Data Sire Residual h Data Sire Residual h set variance variance set variance variance a a CM0 0.00013 0.03339 0.016 CMCR0 0.00013 0.03339 0.016 b b CM30 0.00078 0.09325 0.033 CMCR30 0.00080 0.09432 0.034 b b CM60 0.00092 0.10449 0.035 CMCR60 0.00095 0.10592 0.036 b b CM90 0.00103 0.11429 0.036 CMCR90 0.00107 0.11594 0.037 b b CM120 0.00115 0.12314 0.037 CMCR120 0.00120 0.12504 0.038 b c CM150 0.00128 0.13123 0.039 CMCR150 0.00134 0.13338 0.040 c c CM180 0.00141 0.13877 0.040 CMCR180 0.00147 0.14114 0.041 c c CM210 0.00154 0.14572 0.042 CMCR210 0.00161 0.14831 0.042 a Standard error of the ratios variance component total variance: 0.0003. b Standard error of the ratios variance component total variance: 0.0004. c Standard error of the ratios variance component total variance: 0.0005. 270 B . Heringstad et al. Livestock Production Science 67 2001 265 –272 Table 4

4. Discussion