Introduction
Under most circumstances, the testes and accessory sex glands of the boar are free of bacteria. However, bacterial contamination occurs prior to semen deposition into the cervix and uterus of the female pig. One report indicated that virtually all semen samples are contaminated at the time of collection and mean bacterial counts are highest in the period from July to September.
There are several types of bacteria found in boar semen (see The Swine AI Book). The detrimental roles of bacterial contamination of semen have not been fully explained nor examined. Several preventive measures are used to reduce the likelihood of bacterial contamination and as an extra precaution, antibiotics typically are added to semen extender.
Potential Effects of Bacterial Contamination on Fertility
Bacteria survive quite well in the common extenders, unless antibiotics are added. The ingredients of semen extenders also are used in media prepared for growing or isolating bacteria. For example, 37 grams of glucose are used to make one liter of BTS extender, while 2 grams of glucose are included in one liter of simple media for growing E. coli. Most gram negative bacteria, such as E. coli, Salmonella, and Pseudomonas survive and grow at the recommended storage temperature (15-20º C; 60-65º F) for extended semen. Some reports indicate that metabolic products, such as endotoxin, from some bacteria appear to have detrimental effects on the survival of sperm. Hence, semen quality and the quantity of viable sperm cells may be reduced with bacterial contamination. The likelihood of bacterial growth increases when semen is stored for longer periods prior to use. Storage of semen can act as an incubation period for bacteria.
The direct influence of bacteria on fertilization (conception) remains debatable. The number of bacteria reaching the site of fertilization in the oviduct may be minimal, especially if bacterial counts reflect the step-wise decrease in sperm counts during transit to the oviduct. Conversely, infection of the oviduct is common in sows with endometritis after a natural mating. Several investigations, which were assessing in vitro fertilization, indicated that oocyte fertilization was reduced in the presence of pathogenic organisms in semen. Most producers have observed post-mating, vulvar discharges in sows and gilts. The bacterial infection of the uterus occurred during mating in late estrus. Initially, it was believed that AI would eliminate problems with post-mating discharges; however, poor attention to hygiene in AI programs has resulted in vulvar discharge problems in some sow herds.
Regardless of whether or not bacterial contamination reduces semen quality, interferes with fertilization or causes uterine infections, it is clear that "infected" semen reduces the overall success of an AI program.
Avoid Bacterial Contamination of Semen
To avoid bacterial contamination of the ejaculate during the collection process, a common recommendation is to massage the preputial diverticulum to release preputial fluid and then was the prepuce of the boar before collection. Preputial fluid is grossly contaminated with bacteria. Do not allow preputial fluid to trickle into the collection flask. It is wise to use a new pair of non-toxic gloves for each collection. Contamination of gloves (and semen) occur when the technician wears the same gloves to handle and to collect the boar. Contact with anything other than the boar's extruded penis contaminates the gloves.
As recommended in The Swine AI Book, it is necessary to establish a hygiene policy for all procedures in the AI laboratory. Consider the AI laboratory as an operating room. Everything has to be kept as clean and sterile as possible. Some equipment items, such as the water bath and warming cabinet, produce an excellent environment for bacterial growth and once contaminated, this equipment is an excellent source of bacteria to contaminate other equipment and the semen. A weekly bacterial contamination check of the AI laboratory may be a worthwhile procedure, particularly, if bacterial contamination has been a problem.
Efforts, to maintain strict hygiene during collection and processing of semen, will be a waste of time and money when sloppy techniques are used for the actual insemination. The vulvar area of the sow should be clean and dry and the spiral end of the catheter should be kept sterile.
The Use of Antibiotics in Boar Semen
The inclusion of antibiotics in semen extender has beneficial and detrimental effects. Most studies conducted to evaluate bacteria contamination and the inclusion of antibiotics were conducted in Eastern Europe or Japan in the 1970's and early 1980's. As early as 1968, reports indicated that bacteria were resistant to some antibiotics, such as penicillin-streptomycin. There are numerous types of bacteria in semen and the sensitivity of the bacteria to antibiotics likely is not consistent. Concentrations of antibiotics in the extender are similar to those established for cell and tissue culture.
The selection of the most appropriate antibiotic is a difficult choice. Penicillin-streptomycin (1 gm of each antibiotic diluted in 1 liter extender) was the most common combination. Aminoglycosides, such as gentamicin, neomycin, kanamycin and dibekacin have gained popularity in recent years. The inclusion of aminoglycosides as low as 6 mg in 1 liter of extender was reported to be more effective than the traditional pen-strep combination. Commercial extenders may have 200 mg gentamicin per liter. Newer antibiotics, such as ceftiofur (NaxcelR) and apramycin (ApralanR), currently are being considered for inclusion in extenders.
As most boar studs and producers purchase pre-packaged extender, there is limited choices in antibiotics or the specific quality of a particular antibiotic. Antibiotics, which are included in cell or tissue cultures, typically are very pure and have been assessed for quality. Therefore, these antibiotics are expensive. To determine the sensitivity of a bacterial organism to antibiotics, diagnostic laboratories determine the minimal inhibitory concentration (MIC) of antibiotic that is required to prevent growth of bacteria. The broad spectrum of bacteria in semen make this task difficult, but not insurmountable. Contamination of laboratory equipment often involves few types of organism and the MIC's would be useful.
What We Don't Know
Detrimental effects of antibiotics, including pen-strep and gentamicin, on semen quality and motility were reported by some investigators. There have been few, well-designed studies that examine the bactericidal/bacteriostatic properties of an antibiotic and the effects of the antibiotics on semen quality. The bioactivity and bioavailability of antibiotics are common parameters assessed for an antibiotic intended for systemic treatment of bacterial infections. This means that the blood or tissue concentrations of antibiotic, given at various doses, are determined at different times after treatment. Similar studies are needed to determine if the antibiotics maintain their bioactivity in semen extender for 1-5 days. Furthermore, the shelf-life or expiry date is clearly printed on the labels of injectable antibiotics. Few, if any, packages of semen extender display the expiry date of its antibiotics.
Bacteria are very adaptable and readily change to develop resistance to antibiotics. All producers have observed that their "old reliable" antibiotic fails to effectively treat a particular bacterial infection. This changing resistance of bacteria to antibiotics likely occurs in boar semen. An obvious recommendation would be to assess the antibiotics for your own AI program and procedures. This includes determining the antibiotic sensitivity of the common contaminants and evaluating the effects of the antibiotics on semen quality, motility and subsequent farrowing rates. Certain viruses, such as PRRS virus, have been isolated from boar semen and these viral infections alter the quality of semen for variable periods of time. The roles of the viruses on conception and fertilization and the potential interaction of the virus with bacterial contaminants remain to be elucidated.
Take-Home Message
Suggested Reading
Sone, M. Effects of various antibiotics on the control of bacteria in boar semen. Veterinary Record 111:11-14, 1982.
Almond GW, Britt JH, Carr J, Flowers W, Glossop C, Morrow M, See T. The Swine AI Book. A Field and Laboratory Technician's Guide to Artificial Insemination in Swine. 1994.
