Genetic analysis of in-vitro embryo production traits in Dairy Gir cattle

The potential of dams as oocyte donors can be a selection criterion for animal breeding programs, but also an involuntary driver of the process. In both cases, it is important to determine genetic components influencing the outcome of in vitro embryo production (IVEP). The objective of the present study was to perform a detailed genetic analysis for in vitro embryo production traits in Dairy Gir cows. A dataset containing 11,450 records of ovum pick-up (OPU) and in vitro fertilization (IVF) procedures from 2684 Dairy Gir donors was evaluated. Analyzed traits were number (N_OV) and percentage (P_OV) of viable oocytes; number (N_GI) and percentage (P_GI) of grade I oocytes; number (N_EMB) and percentage (P_EMB) of viable embryos. All analyzes were performed using animal models by a Bayesian framework. Heritability estimates varied from 0.16 to 0.32 for count traits and from 0.01 to 0.06 for percentage traits. The proportion of the total variation represented by the additive genetic effect of sire (semen used in IVF) for N_EMB and P_EMB was 7% and 5% respectively. Associations between estimated breeding values from progeny tested bulls for IVEP traits, milk production, age at first calving and conformation traits were mainly low or close to zero. Results indicate that selection for IVEP traits is possible in Dairy Gir cattle and would not impair genetic progress for traits already considered as selection criteria. The N_OV seems to be a promising target trait. However, a selection index could help to avoid the use of sires with negative genetic merit for percentage traits, minimizing possible deterioration in the long term.