<Li> N is how many children a single sample can give rise to . </Li> <Li> V is the volume of a sample (ejaculate), usually between 1.0 mL and 6.5 mL </Li> <Li> c is the concentration of motile sperm in a sample after freezing and thawing, approximately 5--20 million per ml but varies substantially </Li> <Li> r is the pregnancy rate per cycle, between 10% to 35% </Li>

When was artificial insemination first used in cattle