Potential effects of hormonal synchronized breeding on genetic evaluations of fertility traits in dairy cattle: A simulation study

About 30% of producers use hormone protocols to synchronize ovulation and perform timed artificial insemination (AI) in Canada. Days from calving first service (CTFS) conception (FSTC) become masked phenotypes leading biased genetic evaluations cows for these fertility traits. The objectives this study were (1) demonstrate quantify the potential amount bias evaluations, (2) find a procedure that could remove bias. Simulation was used both objectives. proposed solution identify have been treated by protocols, make their CTFS FSTC missing, multiple trait analysis including traits high correlations with FSTC, which are not affected themselves. A total 12 scenarios (S1–S12) tested, changing percentage herds randomly selected be under AI. Cows given had 86 d 0, evaluation. Four criteria indirectly measure presence bias: correlation between true (TBV) estimated (EBV) breeding values (accuracy); differences mean EBV top 25, 50, 75 sires; (3) changes TBV rankings; (4) over simulated generations. All changed unfavorably proportionally increased accuracy within each class animals (cows, dams, or sires) decreased AI, varying 0.32 (S12) 0.52 (S1) bull CTFS. average sires (best 75, 100 approached population when increasing number animals. sire rank smaller more synchronized animals, going 0.38 0.67 (S1). long-term hormonal clearly generations FSTC. inclusion genetically correlated model effective removing due cows. However, constraints simulation, it is important further investigation real data conducted determine effect AI records dairy cattle.