Birth of live calves by in vitro embryo production of slaughtered cows in a commercial herd in South Africa.

In vitro fertilisation (IVF) has become a useful breeding tool in most of the developed world. In this paper the success of bovine IVF and the birth of live calves under typical South African conditions is reported. Oocytes for IVF were collected from the ovaries of 6 slaughtered Bovelder beef cows. On average, 36.2 oocytes per donor were retrieved. From these oocytes, 43 blastocysts were produced from 5 of the donors by IVF with frozen Bovelder semen. The best 11 of these embryos were transferred into oestrous, synchronised Bovelder recipients in the same herd. As a result, 7 calves were born (a 64% calving rate) from 4 of the original donors. The calves had a normal birth mass, but the mean gestation length of the male calves was significantly longer than the herd average (291.6 versus 285.2 days respectively). No calving difficulties were encountered. In summary, it was shown that IVF for bovine embryo production and transfer is possible on a commercial basis in South Africa.

Aspects of follicle and oocyte stage that affect in vitro maturation and development of bovine oocytes.

Success of in vitro maturation (IVM) and production of bovine embryos as related to aspects of follicle source and oocyte size were evaluated. First, it was determined that bovine oocytes continue growing in all follicular sizes studied, including >1- to 15-mm follicles. Populations of oocytes were collected from surface visible (peripheral) and cortical follicles from the same ovaries. When the number of oocytes from both peripheral and cortical follicles was combined, the yield of oocytes was approximately double that collected from 1 ovarian site alone. Oocytes from cortical follicles were smaller than those from the surface population, and the smaller cortical oocytes had a lower potential for both meiotic maturation and embryo development Only cortical oocytes with the largest diameters underwent IVM and subsequently developed to blastocysts at rates comparable to oocytes from peripheral follicles. As the diameter of the oocytes recovered from peripheral follicles increased, so did their developmental potential. When the stage of the estrous cycle was observed, it was found to have no effect on developmental potential. Finally, oocytes which extruded polar bodies at an earlier time during maturation were, on average, larger than those which extruded polar bodies later. The results serve a practical purpose in assisting selection of oocytes capable of developing into blastocysts and they give useful correlates of oocyte competencies based on knowledge of follicle source and oocyte stage.

Influence of single amino acids on the development of hamster one-cell embryos in vitro.

One-cell hamster embryos placed in culture have always shown a complete block to development at the two-cell stage. In a preliminary study using a chemically defined culture medium containing 20 amino acids (HECM-1), many one-cell embryos were able to escape the "two-cell block" and develop to the four-cell stage. Use of a simpler formulation containing only the amino acids hypotaurine and glutamine revealed marked inhibitory and stimulatory effects of adding the other amino acids. In the first experiment, 19 amino acids were separately examined for effects on one-cell embryo development. Six amino acids (phenylalanine, valine, isoleucine, tyrosine, tryptophan, and arginine) inhibited embryo development (reduced mean cell number; MCN), and three others (glycine, cystine, and lysine) stimulated development (increased MCN), compared with basic medium containing only glutamine and hypotaurine (low control). When the responses with the six inhibitory amino acids were totalled, only 3 of 185 (2%) one-cell embryos reached the six-or seven-cell stage compared to a total of 15 of 76 (20%) embryos that developed to these stages using the three stimulatory amino acids. When tested together in a second experiment, the six inhibitory amino acids significantly reduced the MCN, from 4.28 +/- 0.44 (low control) to 3.71 +/- 0.55. In this group, 17 of 117 (15%) of one-cell embryos reached more than four-cell and only 4 of 117 (3%) reached six- or 7-cell stages, compared with 39 of 117 (33%) and 12 of 117 (10%), respectively, for the basal medium group.(ABSTRACT TRUNCATED AT 250 WORDS)