Abstract
A survey of 169 Holstein-Friesian cattle showed 21 heterozygous for Factor XI activity having activities of .43 .+-. .10 units/ml compared with the normal .99 .+-. .32 units/ml. The frequency of the mutant gene was .06; the 95% confidence limits for the frequency of homozygotes in the population were .1-.8%, and for heterozygotes the frequency was 7.0-16.0%. Test matings indicated this disorder is transmitted as an autosomal recessive gene.