Genetic analysis of reproduction traits and their relationship with conformation traits in Holstein cows

The main objectives of the present study were to examine genetic aspects of fertility traits and their relationships with type traits in Iranian Holstein cows. Fertility traits included calving interval (CI), days from calving to first insemination (DFS), days open (DO), and gestation length (GL). Type traits were stature (ST), body depth (BD), fore-udder attachment (FU), rear-udder height (RU), udder depth (UD), rump width (RW), and angularity (AG). Fertility traits were analyzed using data files containing up to 26,147 records in parities 1 to 8 which were collected from 1980 to 2004. Data on type traits included 3274 records on first lactation cows. An animal model restricted maximum likelihood method was used to estimate (co)variance components. Heritability estimates for fertility traits were low and ranged from 0.04 ± 0.01 (DFS) to 0.07 ± 0.013 (CI) and 0.07 ± 0.002 (GL). Repeatabilities for these traits were estimated to vary from 0.06 (DFS) to 0.12 (GL). Genetic correlations between fertility traits were close to zero. Estimated heritabilities for type traits, except for RU, were moderate and ranged from 0.20 ± 0.047 (FU) to 0.38 ± 0.04 (RW). Genetic correlations between fertility and type traits ranged from zero (DO with ST and FU) to 0.79 (DFS with BD). This study showed that despite the low heritabilities, there was exploitable genetic variance in fertility traits. It showed that body volume traits including BD and AG as well as RW and UD had unfavorable genetic correlations with CI, DFS, and GL. However, these relationships can be used for indirect selection of dairy cows for fertility traits.