Assisted reproductive technologies in cattle: a review.

Over a period of approximately thirty years, commercial bovine embryo transfer has become a large international business. The technology is well established, and more than 500,000 embryos are produced annually from superovulated cows world wide. Since bovine embryos with intact zonae pellucidae can be specified pathogen-free through washing procedures, thousands of frozen embryos are routinely sold and transferred between countries. Throughout the world, approximately 15% of bovine embryos are produced by in vitro technology. Polymerase chain reaction technology is currently being used for sexing embryos on a small scale, and it is likely that this technology will be used for 'embryo diagnostics' in the future. Semen sexing is an established technology and is likely to be used on a small scale in the near future, especially in in vitro embryo production systems. The cloning of adult cattle through nuclear transfer and the production of cloned, transgenic cattle has been technically achieved. However, this is an expensive and inefficient technology, which is being used primarily by the pharmaceutical industry. Benefits in agriculture are likely to be minimal in the near future.