Genetic and phenotypic analyses of milk production and fertility traits of Iranian Holstein dairy cattle

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A data set belonging to Iranian Holsteins from 15 herds (1981 to 2005) were used to investigate the effect of milk production on fertility performance. The traits were: number of inseminations to conception (INS), calving interval (CI), days from calving to first service (DFS), interval between first and last insemination (IFL) days open (DO), and success to first insemination (SF). Cows were divided into three groups (low, medium and high producing) according to milk production. High milk producing group have low fertility performance (P<0.01). High producing group had more 0.37 INS, more 11 days DO, more 17 days CI, more 14 IFL than low producing group. DFS in low producing group was lower than medium and high producing group. SF in high producing cow was 10 % lower than low producing group. Undesirable genetic correlations (<0.37) were estimated between milk production and fertility performance traits. Among fertility traits DFS had lowest (0.17) and CI had highest (0.37) genetic correlation with milk production.  Desirable genetic trend for milk production and undesirable genetic trend for fertility traits were observed. Milk production increased 198 kg per year, INS increased 0.048, IFL increased 1.51days per year and SF decreased 1.37 percent per year. Result of this study indicates that if breeding program only focuses on milk production, fertility performance will decrease. 

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