Impact of Fetal Versus Maternal Contributions of Bos Indicus and Bos Taurus Genetics on Early Embryonic Development

To evaluate maternal and fetal system influence on early embryonic and fetal development in Bos indicus and Bos taurus cattle, a reciprocal embryo transfer approach was used in a completely randomized design with a 2 × 2 × 2 factorial arrangement of treatments in order to generate 55 pregnancies over two consecutive years (n = 55). Recipient cows were placed into the University of Florida Feed Efficiency Facility, containing a GrowSafe feed intake monitoring system, and were assigned randomly to 1) a diet to meet daily maintenance requirements (MAINT), or 2) a diet that restricts intake of nutrients to 70% of energy maintenance requirements (RESTR). Angus (AN) and Brangus (BN) embryo donors were superovulated and artificially inseminated with female sexed-sorted semen from the same breed. Embryos were then randomly transferred 7 d post-insemination (d 7) to either AN or BN recipients fed the respective diets for 20 d. Recipients remained on the dietary scheme until d 91 at which time cows were comingled and fed a common diet that met their energy and protein requirements to the same feeding regime until calving. Transrectal ultrasonography was performed to assess fetal crown to rump length (CRL) weekly from d 42 to d 91. Blood samples were collected weekly from d 28 to d 91 to determine plasma concentrations of pregnancy-specific protein B (PSPB). All analyses were performed using the MIXED procedure of SAS. There was an effect of diet (P < 0.001) and day (P < 0.001) on recipient BW, with RESTR recipients having lower BW than MAINT. Similarly, diet altered recipient BCS from d 70 to d 91 (diet × day, P = 0.005). Embryos from BN donors transferred to recipients fed the RESTR diet resulted in a greater (embryo breed × diet, P < 0.001) plasma concentrations of PSPB. Although no effects of embryo breed (P > 0.05) or diet (P > 0.05) were observed on fetal morphometries, fetuses from AN recipients had greater CRL on d 91 (breed × day, P = 0.021) when compared to BN recipients (167.7 ± 1.8 vs 160.7 ± 1.6 mm, respectively). No effect of recipient breed, embryo breed, or diet were detected on gestation length (P > 0.05) or birth weight of the offspring (P > 0.05). In conclusion, Bos indicus genotype was a significant factor altering concentrations of PSPB during early gestation, whereas Bos taurus recipient genotype positively impacted early fetal growth.