Influence of sexual maturity of donor on in vivo survival of transferred porcine embryos

A study was conducted to determine whether embryos recovered from first-estrous (pubertal) and second-estrous gilts differed in survival when transferred to first- or third-estrous recipients. Embryos were recovered surgically from first- and second-estrous donors 48-72 h postmating and 6-10 normal embryos/zygotes (1-4 cells) were transferred to oviducts (3-5 embryos/ampulla) of nonmated synchronous first- (n = 40) or third- (n = 15) estrous recipients. Blood samples were collected from the jugular vein of recipient gilts on Days 3, 12, and 30 of gestation and the sera were analyzed for progesterone and free (unconjugated) estrogens by use of radioimmunoassays. Recipient gilts were subsequently slaughtered between Days 30 and 40 to assess embryonic losses. Mean number of ovulations was lower among first-estrous vs. third-estrous recipients (8.9 +/- 0.7 vs. 11.4 +/- 0.7; p 0.05). Percentage of recipients that maintained pregnancy was similar between first- and third-estrous gilts (67.5 vs. 60.0%) and recovery of total conceptuses (normal and degenerating) resulting from transfer of one-cell- and cleavage-stage embryos did not differ among first- vs. third-estrous gilts (76.1 vs. 78.2%). Similarly, percentage of viable fetuses in first-estrous gilts that were pregnant from transfer of one-cell- and cleavage-stage embryos was not different from that of third-estrous gilts (69.3 vs. 75.6%). Percentages of total conceptuses and viable fetuses in first- and third-estrous gifts that were recipients of cleavage-stage embryos only also did not differ (p 0.05). However, when source of embryo was considered, percentage of viable fetuses resulting from transfer of embryos of first-estrous gilts was less (63.8%) than that from gilts that had exhibited one estrous cycle (84.9%; p 0.005). Serum concentrations of progesterone were significantly lower in first- vs. third-estrous recipients on Days 3, 12, and 30 of gestation. However, serum-free estrogen in pregnant first-vs. pregnant third-estrous recipients on Days 12 and 30 was not different statistically. Them data indicate that the documented increase in embryonic mortality in gilts bred at pubertal estrus is not due to an abnormal intrauterine environment but rather to a deficiency of the conceptus