PRL and benign prostatic hyperplasia: Serum concentrations of prolactin (PRL), insulin‐like growth factor‐1 (IGF‐1), and 25 hydroxyvitamin D3 (25‐OHD3) were analysed to investigate their possible involvement in the pathogenesis of benign prostatic hyperplasia (BPH) in dogs of two breeds, the Rhodesian Ridgeback (RR) and Labrador Retriever (LR).