Refinement of U.S. Reproductive Performance Evaluations for the Modern Dairy Herd

Abstract

United States (U.S.) national genetic evaluations for reproductive performance include Daughter Pregnancy Rate (DPR), Cow Conception Rate (CCR), Heifer Conception Rate (HCR), and Early First Calving (EFC). Since their introduction, 2003, 2009, 2009, and 2019, respectively, changes in reproductive management (e.g., variable voluntary waiting periods, sexed semen, synchronization protocols, and beef-on-dairy usage) have altered the biological and data structure underlying these traits. In addition, undesirable run-to-run behavior was observed in recent years, including seasonal fluctuations and directional shifts in young bull predicted transmitting ability (PTA).

A comprehensive review of the phenotype pipeline and evaluation model was conducted. Key updates implemented for the April 2026 evaluation include: (1) herd-year and lactation-specific voluntary waiting period adjustment in DPR; (2) introduction of a new trait, First Service to Conception (FSC), defined as days from first insemination to confirmed pregnancy (capped at 200 d with penalty for non-conception); (3) revised CCR and HCR pre-adjustments accounting for service sire breed, mating type, and short-cycle inseminations; (4) stricter daughter age-related inclusion rules to reduce outcome-dependent bias in young bulls; (5) updated contemporary group edits; (6) new variance component estimation; and (7) stricter convergence criteria. DPR, CCR, HCR, and FSC are evaluated in a multi-trait model, while EFC is analyzed separately. Genetic correlations among DPR, CCR, and FSC exceed 0.94, with moderate correlation to HCR.

Across seven consecutive triannual runs from December 2023 to December 2025, the revised system demonstrated improved genetic trend behavior, elimination of systematic downward drift in young bull PTA, and more symmetric run-to-run changes. Traditional PTA distributions by birth cohort better reflect expected selection response. Reranking is trait-dependent and most pronounced for CCR and DPR in low-reliability animals, whereas rankings among young high-reliability bulls (REL ≥95) remain highly consistent (>0.94 Spearman).

Interbull validation requirements were met. The revised evaluation provides improved biological alignment with modern reproductive management while maintaining appropriate stability and interpretability for international comparison.