Oocyte Origin Affects the in Vitro Embryo Production and Development of Holstein (bos Taurus Taurus) - Gyr (bos Taurus Indicus) Reciprocal Cross Embryos.

A reciprocal crossbred embryo production approach was used to assess effects of maternal breed on embryo development in tropical conditions (average temperature 22.0 degrees C and 77.9% relative humidity). Oocytes were recovered by ovum pick-up (OPU) from Gyr and Holstein donors (n = 90 Holstein and 83 Gyr OPUs). Female F1 embryos were produced by fertilization with sperm bearing X-chromosomes from Holstein semen (n = 615 Gyr oocytes) or Gyr semen (n = 255 Holstein oocytes). Blastocysts were transferred to recipients 168 h post-insemination (h.p.i.) (n = 70-144) and there were assessments of pregnancies until birth. Oocyte number per OPU (Gyr 10.0 +/- 0.7 compared with Holstein 6.3 +/- 0.4) and percentage viable oocytes (Gyr 78.8 +/- 1.9% compared with Holstein 71.2 +/- 2.2%) were less for Holstein donor animals. There was a 2.8 fold fewer total number of F1 blastocysts when Holstein donors were used (Gyr: 260, Holstein: 91). Pregnancy assessment during the different stages of gestation indicated the percentage pregnancy was less when embryos were produced from Holstein oocytes (Gyr and Holstein respectively: early pregnancy, 47.9% compared with 38.6%; mid-pregnancy, 44.4% compared with 31.4%; late pregnancy, 41.0% compared with 22.9%). Pregnancy length was also affected by maternal breed (Gyr: 280.8 +/- 0.6, Holstein: 286.3 +/- 0.7). It is concluded that in a tropical environment the maternal breed affects crossbred embryo development with pregnancy rates during the latter stages of gestation being greater when Gyr oocytes are used for production of embryos.