Artificial Insemination

A GROUP of dairymen in New Jersey organized in 1938 the first cooperative in the United States for the artificial insemination of their cows. This method of serving females without natural mating has since become one of the most significant programs for livestock improvement in the history of American agriculture. A great deal of research has been done on all phases. A basic contribution was the invention of the artificial vagina, by which semen is obtained directly from the bull without contamination. After that came the development of the rectovaginal insemination technique, which permits the placement of semen in the cow's cervix or uterus and improves the conception rate. The development of the yolkphosphate diluent made it possible for the first time to store semen for as long as 2 days without seriously affecting its fertilizing ability. The addition of antibiotics to diluted semen improves breeding efficiency and helps to prevent the transmission of certain reproductive diseases. Adoption of the photoelectric colorimeter for determining sperm concentration permits maximum dilution of semen without lowering breeding efficiency. One of the newest developments, the freezing of semen, makes it possible to store diluted semen for indefinite periods. Improvements in semen diluents, methods of handling semen, and insemination techniques have enabled most studs to maintain breeding efficiency equal to or slightly higher than natural service. A shortcoming of artificial insemination used to be that a sire could be made available to dairymen only about 2 days each week. Semen was collected from a bull at weekly intervals, and satisfactory fertilizing capacity could not be maintained for more than 2 days. We have learned how to freeze bull semen without destroying its fertilizing capacity. By adding glycerol as a protective agent, then freezing and storing diluted semen at extremely low temperatures ( — 110° F. with dry ice or —320° with liquid nitrogen), fertihty can be maintained for several years. The use of frozen semen makes it possible to have semen from each sire available every day. It facilitates the long-distance transportation of semen. It permits more cows to be bred to some bulls, as a ''bank" of semen can be accumulated during periods of light demand. Cows can be mated to a bull during extended periods of sexual inactivity or after the bull is dead. Thirteen studs were using frozen semen for their entire oper-