Impact of assisted reproduction techniques on subsequent reproductive performance of dairy heifers and lactating cows.

Use of assisted reproduction techniques (ART) such as ovum pick-up for in vitro embryo production (OPU-IVP) and multiple ovulation for embryo transfer (MOET) in livestock has increased in recent years. Objectives of this retrospective cohort study were to evaluate the association between ART and reproductive performance of donor dairy heifers and cows until third lactation. Holsteins donors subjected to MOET (n = 1087) or OPU-IVP (n = 551) were matched with non-donor females (n = 4112) based on date of birth allowing for a maximal difference of 10 days. Binary variables were analyzed using multivariable logistic regression whereas time to first breeding and time to pregnancy were analyzed using multivariable Cox's proportional hazard models and Kaplan-Meier survival curves. Contrasts were built to assess the association between donor status (non-donor vs. MOET + OPU-IVP), type of ART (MOET vs. OPU-IVP) and number of OPU-IVP procedures. Non-donor heifers had greater hazards of first breeding, pregnancy, and first calving compared with donor counterparts. Proportion of pregnant heifers after first breeding was reduced for donors compared with non-donors, which was primarily explained by a reduced proportion of OPU-IVP donors that became pregnant. Although proportion of pregnant cows after first breeding was not associated with ART group during first lactation, hazards of first breeding and pregnancy relative to the end of voluntary wait period were reduced for OPU-IVP donors. During second and third lactations, hazard of first breeding was greater for non-donors compared with donor counterparts. However, proportion of pregnant cows after first breeding and pregnancy hazard were not associated with ART groups. Culling was greater for non-donors compared with donors across all lactations. However, proportion cows culled during first lactation that was attributed to reproductive causes tended to be greater for donor compared with non-donor cows. Assisted reproduction techniques were associated with reduced reproductive performance in dairy heifers and cows but did not increase overall culling.