Boar semen is a biological fluid produced by male pigs, known as boars, containing the reproductive cells necessary for fertilization. This fluid plays a fundamental role in the propagation of pigs, facilitating genetic transfer from boar to sow and initiating pregnancy.
Biological Characteristics of Boar Semen
Boar semen consists of two main components: spermatozoa and seminal plasma. Spermatozoa are the male reproductive cells, while seminal plasma is the fluid portion that transports and protects them. A typical boar ejaculate volume ranges from 50 to 400 milliliters, averaging around 250 milliliters, making it one of the largest among domestic animals. Normal boar sperm features a head containing genetic information and an acrosome with enzymes for egg penetration, along with a tail for motility.
Sperm concentration in boar semen can vary widely, from 10 million to 1 billion spermatozoa per milliliter, though dense ejaculates often contain between 0.151 and 0.400 billion spermatozoa per milliliter. Sperm motility, the ability of sperm to move, indicates semen quality; a “wave” motion suggests good quality. Semen color is white with bluish shadows, and the pH of the main fraction is around 7.21 to 7.69 immediately after collection.
Importance in Swine Breeding
Boar semen is important in modern swine production, particularly through Artificial Insemination (AI). AI allows for the extensive use of genetically superior boars, accelerating genetic improvement within pig herds. This means desirable traits, such as faster growth rates or improved meat quality, can be disseminated across a larger population more rapidly than with natural mating.
The use of AI with boar semen offers benefits in disease control, as it minimizes direct animal-to-animal contact, reducing the risk of transmitting infectious diseases. AI enhances reproductive efficiency by allowing fewer boars to service a greater number of sows, leading to reduced feed and maintenance costs for producers. For instance, a single boar can provide enough semen to inseminate hundreds of females annually, a feat impossible through natural service.
Collection and Preparation for Artificial Insemination
The collection of boar semen employs the gloved hand technique, where the boar mounts a dummy sow in a designated collection area. During collection, the initial pre-sperm fluid is discarded to avoid contamination. The gel fraction, a characteristic component of boar semen, is filtered out using sterile gauze or a mesh filter. The collection container, often an insulated thermos, is pre-warmed to approximately 38°C to prevent cold shock to the sperm.
Immediately after collection, the ejaculate volume is measured, and the semen is evaluated for initial quality parameters such as motility and relative sperm concentration using a microscope. For liquid storage, the semen is diluted with an extender, such as Androhep Plus or Androstar, at a 1:1 ratio. This diluted semen is then gradually cooled to 15°C before being stored at around 17°C for up to 5 days.
Factors Influencing Semen Quality
Several factors influence the quality and viability of boar semen. The boar’s age plays a role, with optimal semen quality observed in boars between 10 and 30 months of age; quality may decline after 35 months. Environmental factors, particularly temperature, can affect semen quality; heat stress can lead to decreased ejaculate volume, reduced sperm motility, and an increase in abnormal sperm morphology.
Nutrition is also a factor, as adequate dietary energy and specific supplements, such as L-leucine and fat-soluble vitamins, can improve semen volume, sperm motility, and overall sperm quality. Diseases like brucellosis, erysipelas, or certain mycoplasma infections can cause orchitis, leading to damaged testicles and reduced semen production. The frequency of semen collection can influence ejaculate volume and sperm concentration, with intensive collection potentially causing a decrease in total sperm count.