T R a N S F E R of B O V I N E D E M I - E M B R Y O S W I T H a N D without the Zona Pellucida 1

Bisected bovine embryos with or without the zona pellucida were transferred to recipients nonsurgically in five field trials. Embryos were collected from superovulated donors 6.5 to 7.5 d after estrus; only embryos of good and excellent quality were bisected. Demi-embryos were transferred either within a zona pellucida, without a zona pellucida, or in the third and fourth trials, without a zona but embedded in 7% gelatin. Pregnancies were diagnosed at 44 to 68 d of gestation. In a preliminary trial, 9/29 zona peilucida-intact demi-embryos developed into fetuses compared with 1/10 zona pellucida-free demi-embryos (P>.I). The proportion of zona-free demi-embryos developing to fetuses was not significantly different from the zona-intact group in the second trial either, 24/49 and 5/19, respectively. In trial 3, the proportion of zona pellucida-free demi-embryos developing was 8/25; of zona-enclosed embryos, 29/88; and of zona-free demi-embryos embedded in gelatin, 8/22 (P>.l). Similarly, in the fourth trial the rate of development of zona-free demiembryos to fetuses was 5/12, that of zona-enclosed embryos was 32/81, and that of zona-free demiembryos embedded in gelatin was 3/12 (P>.I). In trial 5, survival of zona-enciosed demi-embryos to fetuses was 40/105, and of zona-free demi-embryos, 46/109 (P>.l). Except for trial 2, half of the demi-embryos were twinned, one to each uterine horn; twinning did not significantly affect the proportion developing to fetuses for any of the demi-embryo groups. It is concluded that placing post-compactinn demi-embryos into the zona pellucida for transfer does not improve pregnancy rates significantly. (