A method of producing pharmaceutical proteins in semen is reported in Nature Biotechnology (1999;17:1087). Male transgenic mice that secrete human growth hormone into their ejaculate have been produced. The amount of protein in each millilitre of ejaculate was less than with other transgenic systems, such as goats' milk, but the authors suggest that there may be ways to achieve higher expression, such as by using boars.
Meanwhile, New Scientist (November 13, p25) reports that two drug companies have produced genetically engineered chickens which lay eggs from which extraction of drugs is possible. Hens produce an average of 200 eggs each year and, in each egg, 100mg or more of drug is claimed to be produced.