Embryo transfer in cattle experience of twenty-four completed cases

Thirty-nine potential embryo transfer and 13 ovum collection experiments were initiated within a small experimental herd of mainly nulliparous cattle. Donors for 50 of the experiments were treated with pregnant mares' serum gonadotrophin (PMSG) with or without human chorionic gonadotrophin (HCG) to induce superovulation. Optimal responses (3–20 ovulations) occurred in 56.4 % of treated animals; there was some evidence of reduced responsiveness to repeated treatment. Overall ovum and embryo recovery rate at slaughter or laparotomy was 46.3 % but in some experiments exceeded 80 % on Days 4 and 5 after estrus. Recovery rates were adversely affected by previous surgery and by excessive ovulation rates. 73% of recovered ova were fertilized. Only 20 of the 39 potential transfer experiments were completed, 15 of the 19 incomplete experiments being due to donor failures (lack of superovulation in 11 cases, no fertilization in four). Transfers of three embryos (one case), two embryos (19 cases) or one embryo (four cases) were made surgically to 24 recipients. Of the first 10 recipients, one conceived; of the last 14, ten (71.4%) did so. Best, results were obtained by collecting ova on Day 5 or 6 and using recipients within one day of being synchronous with the donor. Embryos collected at slaughter gave results as good as did those collected surgically. Ten of the pregnant recipients had received more than one embryo but only four gave birth to more than one calf. Some problems associated with the practical application of this technique are discussed.