AbstractThe main objective of this study was to estimate genetic correlations between fertility and production in first and second lactations as well as between fertility traits measured in the same way at different ages. The analyses were carried out for Swedish Red and White cows born from 1986 to 1996, in total about 578 000, 430 000, and 221 000 records in the heifer period, first lactation and second lactation, respectively. The fertility traits studied were: interval between calving and first insemination (CFI), interval between calving and last insemination (CLI), number of inseminations per service period (NINS) and number of treatments for reproductive disturbances (NREPT). Production was measured as the average of the energy-corrected milk yield from the second and third test-days in a lactation (ECM23). A linear, bivariate model that included effects of herd-year, month, age, and sire of the cow was applied. A relationship matrix containing sire and maternal grandsire of the sire was included. The (co)variance components for the random effects were estimated by use of a restricted maximum likelihood algorithm. The genetic correlations between fertility traits and production within first and second lactation were in the range of 0.1 to 0.3, all of them unfavourable. However, the genetic correlation between NREPT and ECM23 was close to zero within both lactations. The heritabilities, calculated without the herd-year variance included in the phenotypic variance, varied between 0.02 and 0.06 for the fertility traits with only minor differences between first and second lactation. The heritability of ECM23 was 0.35 in the first lactation and 0.28 in the second lactation. The genetic correlation between NINS during the heifer period and in first lactation was high, 0.7. The heritabilities for NINS and NREPT during the heifer period were very low, <0.01. In conclusion, there were only minor differences in inter-relationships between fertility and production in first and second lactation and the traits were negatively associated with each other. Based on the genetic correlation between NINS in the heifer period and NINS in first lactation, this study indicated that the traits at least partly are regulated by different sets of genes.
Clinical Mastitis in Norwegian Cattle: Frequency, Variance Components, and Genetic Correlation with Protein Yield
