Factors affecting conception rate of Israeli Holstein cattle.

Environmental and genetic effects on reproductive performance were estimated. Data included records of 194,579 inseminations of cows and 56,132 inseminations of heifers in 200 kibbutz herds from 1980 to 1981. Conception status was ascertained by veterinary palpation if no subsequent parturition was recorded. With subsequent parturition, the insemination closest to 277 days before parturition was considered successful. Largest differences in conception rate were between cows (40.4%) and heifers (64.3%) and among insemination month for cows (23.5 to 51.5%). Heritabilities of sire effect on conception rate were .016 for cows and .006 for heifers. Correlations between heifers and cows were .64 for inseminator and .54 for service sire. Low correlation between heifers and cows for herd effect (.17) indicates a management problem; low correlation between heifers and cows for sire effect (.27) suggests a different genetic mechanism for fertility. Significant improvement may be achieved in fertility by selection of service sires, sires, and inseminators if evaluations are based on a large number of observations. However, the major increase of conception rate may be expected from reducing adverse effects of summer conditions on reproductive performance.