Phenotypic and genetic evaluation of stillbirths in United States Holsteins
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Stillbirths, death of a calf within 48 h of parturition, create great economic losses to the dairy industry. The objectives of this research project were to determine: 1) if there have been changes in the rate of stillbirths in United States Holsteins, 2) the genetic and environmental factors that influence the occurrence of stillbirths, and 3) whether stillbirths are the same trait in primaparous and multiparous cows. Chi-squared Automated Interaction Detection algorithm was used to determine the most significant factors that affect the rate of stillbirths. Parity of the dam was the most significant factor; 11.0% in primaparous and 5.7% in multiparous cows. The second most significant factor was dystocia. As dystocia increased from 1 (= no assistance) to 3 (= needed assistance), so did the incidence of stillbirths, 6.1, 14.3, and 27.7% in primaparous cows; 3.9, 12.6, and 26.5% in multiparous cows. Inadequate maternal preparation for parturition was suggested as the cause of the continued increase in stillbirths.A mixed logistic regression analysis identified a significant increasing trend in the odds of a stillborn calf from 1985 to 1996; 4.1% per yr in primaparous cows, and 2.4% per yr in multiparous cows. The estimate of heritability for sire of the calf was 1.1% using data for primaparous cows and 1.5% for data for multiparous cows. Maternal grandsire heritability estimates were 2.2% for primaparous cows; 0.8% for multiparous cows. Despite the low genetic variance for stillbirths, there was a large range in PTA. Sire evaluation for survival can identify particular sires with low survival among their progeny. Herd-year variances were larger for all data sets than sire and maternal grandsire variances. Genetic change in the mean PTA for stillbirths was quite variable from year to year. There was no evidence of a genetic trend. Stillbirth rate should be monitored on an annual basis in Holsteins.