Use of milk samples from a milk evaluation program for the genotyping of cows

Milk can be an attractive DNA-resource for genotyping milking cows, e.g. for paternity control or QTL analysis within a daughter design. The use of milk collected within the established milk evaluation programs enables the collection of large numbers of samples. Nevertheless, there are limitations when using the remedies of tested milk samples, e.g. permutations of samples or partially degraded DNA. A DNA preparation method suitable for samples from routine milk recording has been developed that combines an initial centrifugation step with direct lysis of cells and purification from comparatively high volumes by using silica membrane spin columns. The method yields high quality genomic DNA from fresh samples and PCR grade DNA from remedies of tested samples. In addition the potential use of milk samples within a daughter design was evaluated. We collected reference samples from 119 Simmental dairy cows from 6 half sib families. From 89 of these dairy cows remedies of milk samples were obtained from the routine milk laboratory. Paternity could be established by microsatellite analyses for all 119 reference cases. From the 89 milk laboratory samples 86 were successfully microsatellite typed. In 81 cases the genotypes from milk and reference sample were identical. In summary it could be shown that it is possible to genotype dairy cows from test laboratory milk samples, but results have to be used carefully taking into account inherent limitations. The use of milk as compared with tissue samples as a source for DNA within daughter designs is discussed.