Comprehensive Insight into the Male Dog Reproductive System in Health and Diseases: Developmental, Genetic, and Environmental Factors—Review on Research and Clinical Trials

As in other mammalian species, the complex and specific interactions between internal biological processes and external factors regulate and impact the male dog reproductive system functions. This comprehensive review integrates physiological and molecular mechanisms underlying the reproductive system maintenance throughout the anatomical and histological structure of reproductive organs and their functions from development to aging. Simultaneously, the presentation of fundamental hormonal regulations and functions of the reproductive system is comprised. Special attention is put on e.g., genetic, developmental, age- and environmental-related disorders. The structural and hormonal status of the reproductive organs in response to single or mixed influences: genetic predispositions (e.g., cryptorchidism, sex chromosome aneuploidy syndrome), developmental courses (e.g., cryptorchidism, uterus masculinus, hypospadias), age-related diseases (e.g., tumors), and environmental stressors: e.g., endocrine-disrupting chemicals, toxins, heat stress (possibly leading to e.g., hypogonadism, cryptorchidism, infertility, tumors, precocious aging) is provided. Such multidirectional and comprehensive associations of grouped, selected, clinically significant pathological processes and diseases are broadly considered and linked here for the first time. Based on both epidemiological and experimental findings, the etiologies, current diagnostic approaches, treatment options, and prognostic assessments of these common male dog disorders are presented. This compendium seems useful for young veterinarians, researchers, breeders, and dog owners, enabling them to integrate knowledge on biological principles and processes with clinical practices and research in recent and future canine andrology.