Monitoring for bacteria in boar studs

Monitoring bacteria in a boar stud is an important quality control step.

Failure to control bacterial loads in the end product leads to reduced shelf life and agglutination problems in stored semen. This leads to increased returns and poor fertility. Although improper timing of insemination is the primary factor for vaginal discharges and uterine infections, contaminated semen can provide the opportunistic component.

Antibiotic additives
Most semen extenders for swine include gentamicin sulfate as an additive to control bacteria. Other common antibiotics in use include linco‑spectin, neomycin and ceftiofur. It is  important to know what antibiotics are included in the extender. If bacteria are found in extended semen, a minimum inhibitory concentration (MIC) should be determined to see which antibiotic can be added to control those specific bacteria.


 Boar studs should be routinely cultured for bacteria to provide information about the sanitation level of the stud and lab, as well as continuous monitoring of the semen that leaves the stud.

Culture routine
Boar studs should be routinely cultured. The most important item to culture is extended ejaculates. I recommend culturing extended ejaculate samples from each collection day.

Many of the studs in our practice send in four doses from each collection day, which we streak out on 5 percent blood agar plates on day four after collection. Regular monitoring like this gives a good indication of the sanitation level of the stud and lab as well as continuous monitoring of the semen going out.

In addition to extended semen, certain areas of the lab should be cultured on a monthly basis. The areas to emphasize  include anything that touches semen or extender, and any area that is warm and/or moist. Lab equipment that touches semen or extender is important to monitor because contamination of such equipment could result in contamination of the entire day"s production.

This could include:

  • Water system
  • Pipette tips
  • Extender
  • Extender vats
  • Extender bags
  • Tubing used to transport semen or extender
  • Semen dispensing equipment
  • Thermometers

Those areas of the lab that are warm and moist are high risk because a warm, moist environment promotes bacterial growth. Con-tamination in one of these areas results in explosive growth in a matter of hours and can be easily tracked all over the lab. Warm, moist areas of concern would include:

  • Water baths
  • Slide warmers
  • Warming boxes

All of these areas should be cultured after cleaning to check the sanitation procedures. There should be no growth.


 Certain areas of the laboratory should be cultured for bacteria on a monthly basis. The areas to emphasize include anything that touches semen or extender and any area that is warm or moist.

Raw ejaculates can also be cultured to see what kinds of bacteria are entering the lab with the ejaculates. Expect to see a wide variety of growth on these samples. The value of culturing raw ejaculates is to confirm the source of a certain isolate obtained in the lab or in extended semen.

A bacterial swab with Amies media works well when taking the sample at the stud. The swab can then later be streaked onto 5 percent sheep blood agar. I put four on one plate (each in its own quadrant) to save cost.

If sampling water, day 0 semen, or day 1 semen, pre‑incubation overnight in the Amies media is recommended to increase the sensitivity. Other samples can be cultured directly.

There should be no growth on extended semen samples or on any of the equipment listed above. If there is growth, sensitivity/MIC testing should be done to see which antibiotics could work. You also should re-evaluate sanitation procedures.

Common bacteria
When bacteria are cultured in extended samples, it is most often a single bacteria. It is important to forward the culture to a reference lab for positive identification because most of the isolates are not commonly identified in pigs. MIC testing should also be done. Cultures done at the Swine Vet Center on ten boar studs over the last seven years have yielded the results shown in Table 1 (on page 9).


Minnesota swine veterinarian Darwin Reicks, with Swine Vet Center P.A., St. Peter, believes that routinely monitoring bacteria in a boar stud is a critical quality control step.

Studies reported by G. C. Althouse showed the most frequently isolated bacteria on 23 field investigations to be from enteric (Enterobacter eloacae, Escherichia coli, Serratia marcescens) and non‑enteric (Alcaligenes xylosoxydans, Burkholderia cepaceia, Stenotrophomonas [Xanthomonas] maltophilia) groups.

Routine cultures from ten different boar studs over the last seven years at the Swine Vet Center have yielded the bacteria listed in Table 2 (at right).

Monitoring semen for bacterial contamination should be a routine part of a herd health program at a boar stud. Further, ensuring that the antibiotics in the extender are working will prevent potential losses at the sow farm due to reduced fertility.   

Editor"s note: The author is a swine veterinarian with Swine Vet Center, P.A., a multi-person swine-only veterinary clinic and consulting service located at St. Peter, Minn. Information in this article was originally presented at the 2003 University of Minnesota Allen D. Leman Swine Conference.



Restricted HTML

  • Allowed HTML tags: <a href hreflang> <em> <strong> <cite> <blockquote cite> <code> <ul type> <ol start type> <li> <dl> <dt> <dd> <h2 id> <h3 id> <h4 id> <h5 id> <h6 id>
  • Lines and paragraphs break automatically.
  • Web page addresses and email addresses turn into links automatically.