MILK AS A SOURCE OF DEOXYRIBONUCLEIC-ACID AND AS A SUBSTRATE FOR THE POLYMERASE CHAIN-REACTION

Somatic cells in milk were used as a source of DNA and as a substrate for the polymerase chain reaction. Successful DNA extraction required a minimum total of 17 x 10(6) cells in the milk sample. The DNA yield per cell was highly variable but comparable, on average, with the yiel d from peripheral blood leukocytes. In all cases, direct polymerase ch ain reaction on milk samples, using a variety of primer pairs, yielded amplified products of correct size that were identical to those obtai ned by polymerase chain reaction of purified DNA extracted from milk o r blood. Milk and DNA extracted from milk served as substrates for dir ect sequencing of part of the bovine growth hormone gene. Milk samples with added preservative were stored over 200 d without effect on the polymerase chain reaction. Thus, milk can often substitute for blood a s a source of DNA for Southern blot analysis and is a preferred substr ate for the polymerase chain reaction. The technical convenience of mi lk as a source of DNA can be expected to increase the field of applica tion of marker-based methods for genetic analysis and genetic improvem ent of economic traits in dairy cattle.