Relationship of Reproductive Factors with Interval and Rate of Conception

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Abstract
The relative importance of several reproductive traits on the variation in interval and rate of conception was determined. The average conception interval of all cows was 146 days, or 122 days excluding 49 open infertile cows that were assigned arbitrarily a maximum 308 day conception interval. The conception rate was 87%. Least squares models, including the fixed effects of season, parity, uterine involution grade, ovarian condition, retained placenta, dystocia, embryonic deaths, reproductive treatment and times bred, explained 75% of the variation in conception interval and 71% of the variation in conception rate. More breedings, embryonic deaths, and reproductive examinations and poor uterine involution grades were associated with longer conception intervals. The occurrence of luteal cysts was associated with shorter conception intervals. Longer conception intervals and lower conception rates, characteristic of open infertile cows, were associated with lower milk production. In general, the significant correlations among the reproductive traits were positive, but most correlations involving conception rate or deviation milk with other reproductive traits were negative. Many traits, including conception interval, conception rate, calving assistance, 30 day reproductive treatment, 30 day uterine involution grades, cystic follicles and reproductive exams had repeatabilities around 0.20.