Gene expression of mammary tissue was performed by extracting RNA with a PureLink RNA Mini Kit (Life Technologies, Carlsbad, CA), and subsequent cDNA synthesis was conducted by RT, where the total RNA (1.0 μg) was reverse-transcribed in a final volume of 20 μL employing the Improm II kit (Promega, Madison, WI). In summary, the protocol began with the incubation of RNA with 0.5 μg oligo-dT for 5 min at 70°C. Then, 1× buffer, 3.0 mM MgCl2, 0.5 mM dNTP, 40 units of RNase inhibitor, and 1.0 μL of Improm reverse transcriptase were added to the reaction tube. The reaction was conducted at 42°C for 60 min, followed by 15 min cooling at 70 and 4°C. Then, the samples were subjected to RT and subsequent analysis of the amplified gene fragments. The expression of the target genes was determined by RT-PCR using the primers described in Table 1.