Abstract
Embryos were collected non-surgically from superovulated Holstein cows on day 6 to 7.5 post-estrus. Fifty-three embryos classified as good-to-excellent were bisected microsurgically. Viability of the half-embryos was assessed by blastulation in vitro or development into calves.
Twenty-nine day 6-6.5 embryos were bisected with a fine glass needle, and 52 half-embryos (25 pairs) were produced. Twenty-nine (13 pairs) of these half-embryos were cultured for 24 to 36 hours, and 28 (12 pairs) of which were developed, including 4 trophectodermal vesicles. Ten pairs of half-embryos were transferred non-surgically to 10 recipients, and two recipients were pregnant at day 60. One of them calved only one female, but another aborted on day 60 to 120.
Day 7.5 embryos were bisected by three different methods. In method a), eight embryos were bisected with a fine glass needle, and 12 half-embryos (6 pairs) were produced. These half-embryos were cultured for 2 to 12 hours, and three (no pairs) of which were developed. Transfer was not carried out. In method b), three embryos were bisected with a machined surgical blade, and four half-embryos (2 pairs) were produced. These were cultured for 2 to 12 hours, and all of which were developed. Transfer was not carried out. In method c), thirteen embryos were bisected with a razor blade and a fine glass needle, and 25 half-embryos (12 pairs) were produced. Nineteen (9 pairs) of these half-embryos were cultured for 2 to 12 hours, and four (1 pair) of which were devel-oped. Two pairs of half-embryos were transferred non-surgically to two recipients, and one recipient calved a set of normal male monozygotic twins. Two half-embryos of a monozygotic pair were trans-ferred surgically to two recipients, but no pregnancy was obtained.
