We examined the sexual development and insemination capability of boars representing five breeds used at Polish sow insemination stations. The speed of attaining full breeding maturity by the boars and their insemination usefulness was assessed based on the results of experiments analysing age-related changes in the physical characteristics of the ejaculates. Directly after sampling, the ejaculates were analysed for the following physical parameters: ejaculate volume, sperm concentration and the percentage of progressively motile spermatozoa per ejaculate. The total number of spermatozoa in the ejaculates and the number of insemination doses obtained from one ejaculate were calculated using SYSTEM SUL v. 6.1 software. The sexual development of boars continues during insemination use, leading to improved ejaculatory performance. The physical parameters of the ejaculate change along with the age of the boar. The Duroc and Hampshire boars represent a pattern of sexual development that is different from that of the PLW, PL and Pietrain males, with an evident earlier termination of growth. The American boars (Duroc and Hampshire) acquire top ejaculatory performance approximately 6 months earlier.