A boar is defined as a mature male pig. The study of its reproductive system is foundational to agricultural science, as the efficiency of swine reproduction directly impacts the global pork supply chain. This biological machinery allows for the rapid dissemination of desirable genetic traits across commercial herds. The boar’s reproductive success relies on specific anatomical features, highly ritualized behaviors, and distinct semen characteristics.
Unique Boar Reproductive Anatomy
The boar possesses a fibroelastic penis, characterized by rigidity and limited diameter increase upon erection. This rigidity is maintained by dense connective tissue, allowing the penis to extend by straightening the pre-scrotal S-shaped curve, known as the sigmoid flexure. The glans penis forms a corkscrew or spiral shape that rotates counter-clockwise. This specialized tip is designed to lock securely into the folds of the sow’s cervix during copulation.
The accessory sex glands—including the seminal vesicles, prostate, and large bulbourethral glands—contribute significantly to the large ejaculate volume. The bulbourethral glands secrete the thick, gelatinous material expelled during the final stage of ejaculation.
Natural Mating Behavior and Copulation
The mating process begins with a distinct courtship sequence. The boar performs tactile stimulation, such as nudging the sow’s flanks and emitting specific vocalizations, known as the “boar grunt,” to encourage the standing reflex. Once the sow stands firm, the boar mounts rapidly. Intromission occurs when the spiral-tipped penis enters the sow’s reproductive tract. The corkscrew glans rotates and locks into the folds of the cervix, preventing backflow of the high-volume ejaculate. This physical lock initiates an extended period of ejaculation, often lasting between three and twenty minutes, with an average around four to five minutes. During this time, the sow remains immobile, allowing the boar to deposit the semen directly into the cervix and uterus.
Characteristics of Boar Semen
Boar semen is characterized by its high volume and fractionated nature, resulting from accessory sex gland secretions. Average ejaculate volume ranges from 150 to 250 milliliters, though it can vary widely. The ejaculate is released in three distinct phases: the pre-sperm fraction, the milky-white, sperm-rich fraction, and the post-sperm gelatinous fraction. The sperm-rich phase contains the vast majority of spermatozoa and is the fraction primarily used in artificial insemination (AI). The final fraction is a thick, sticky gel produced by the bulbourethral glands. This gelatinous material serves as a physiological plug that seals the sow’s cervix after mating, preventing the backflow of semen.
Role in Modern Swine Production
Artificial Insemination (AI) is the preferred method in commercial swine production worldwide due to the unique characteristics of boar reproduction. AI allows producers to maximize the genetic influence of superior boars, as a single ejaculate yields enough doses to inseminate multiple sows. This technique also significantly reduces the risk of disease transmission, a major concern in large-scale farming.
Semen is collected using the gloved-hand technique, often with the boar mounting a stationary dummy sow. Once collected, the ejaculate is immediately filtered to remove the gelatinous plug. It is then evaluated for quality, focusing on motility, concentration, and morphology. Boar semen is highly sensitive to temperature and is typically used fresh after being extended and stored between 15 and 20 degrees Celsius. This careful processing and storage allows for the widespread distribution of high-quality genetics, underpinning modern pork production.