A functional genomic approach to the study of the milking ability in dairy sheep

To understand the mechanisms underlying milk ability and more precisely the kinetics of milk emission, we compared teat transcriptome profiles from Lacaune ewes in the tails of the milk flow phenotypic distribution. Two different arrays containing respectively 1896 and 13 168 PCR products selected from several tissue-specific cDNA libraries, including mammary gland, allowed the identification of 73 differentially expressed genes between teats from high and low milk flow ewes. Genes involved in muscle contraction were identified as over-expressed, and genes encoding collagen were found to be under-expressed in teats from low milk flow ewes. We confirmed this underexpression of COL1A1 and COL1A2 in low-milk flow ewes using RT-qPCR. These results suggest that milking ability may be due to the capacity of the teat sphincter to relax during mechanical milking. We propose that an optimal condition for mechanical milking may require proper relaxation of the teats. To our knowledge, this is the first transcriptomic analysis studying milking ability, using udder tissue for gene expression profiling, which demonstrates that mechanical milking ability is not only determined by morphological features but also by tissue composition.