Boar taint is the offensive odor or taste that can be evident during the cooking or eating of pork or pork products derived from non-castrated male pigs once they reach puberty. It is only found in a small minority of pigs and can be found in both males and females as the chemicals that cause the smell are produced in the intestines as well as the testicles.
Studies show that about 75% of consumers are sensitive to boar taint so it is necessary for pork producers to control it. Women appear to be more sensitive than men and some ethnic groups also seem to be more sensitive than others. About 25% of consumers cannot detect the taint chemicals and about 80% of boar pigs do not have taint. Selecting pigs for breeding that do not have taint and managing on pasture virtually eliminate any chance of boar taint and have been successfully used at many farms.
Controlling boar taint
For centuries, pigs in some countries have been castrated to prevent boar taint which can show up in a small percentage of boars in some breeds. Most boar pigs do not have boar taint and are slaughtered before puberty so it is not an issue. The long-standing practice in some countries sees male piglets castrated when they are 2–3 weeks old, while on many American farms castration typically occurs 2–3 days after birth.
In some countries, such as Australia, pigs are slaughtered at a younger age. This is because the two natural substances that cause boar taint – androstenone and skatole – only start to accumulate in the fat of male pigs when they sexually mature. Skatole can actually show up in female as well as male pigs. It is produced by bacterial action in the intestines and deposited in the fat independently of castration – this is a management issue. Pigs raised on pasture do not have this problem although it is common to pigs raised in confinement settings. Slaughter at the standard six month age can help reduce the presence of skatole based boar taint and adrostenone based taint.
Another possible method to control boar taint is to select the sex of the piglet before birth in an attempt to breed only female pigs, using sorting based on sex chromosome and artificial insemination. This method has been successfully used in cattle breeding but the technique is still under research and no economic or practical solution yet exists in pig production.
Boar taint is caused by the accumulation of two compounds – androstenone and skatole – in the fat of a minor number of male pigs. Most pigs do not have boar taint and it is rare by slaughter weight age.
Androstenone (a male pheromone) is produced in the testes as male pigs reach puberty, while skatole (a byproduct of intestinal bacteria, or bacterial metabolite of the amino acid tryptophan) is produced in both male and female pigs. However levels are much higher in intact boars because testicular steroids inhibit its breakdown by the liver. As a result, skatole accumulates in the fat of male pigs as they mature.
As castration has received criticism in recent years, some producers and producer associations are seeking alternative methods to control boar taint. Some producers are breeding out the taint and avoiding the few breeds of pigs that are high in taint. Yorkshire, Hampshire and other lighter colored pigs are known to be particularly low in the androstenone based taint while Duroc pigs are high in the taint. When pigs are raised on pasture in a rotational grazing system, similar to cattle, goats and sheep, the skatole based taint does not occur because the pigs are on fresh ground and not inhaling and eating their own feces.
Vaccination against boar taint, which has been used in Australia and New Zealand since 1998, is a  solution that uses the pig's immune system to control boar taint. The use of the vaccine is claimed to be as simple and reliable as physical castration in controlling boar taint. It can be administered by trained farm personnel and enables the production of pork meat that is claimed to be of high quality and to be safe for consumers to eat.
The vaccine works by stimulating the pig's immune system to produce specific antibodies against gonadotropin-releasing hormone (GnRH). This temporarily inhibits testes function and thus stops the production and accumulation of boar taint–causing compounds.
By stimulating production of antibodies specific to GnRH, the vaccine stops the chain of events that lead to the release of testosterone and other steroids from the testes, including androstenone, one of the two causes of boar taint. The other major taint-causing compound, skatole, is also eliminated because the lower steroid levels allow the liver to more efficiently metabolise it.
Each pig must be immunised twice to successfully control boar taint. The timing of the first dose is relatively flexible, but there must be a minimum of four weeks between the two doses, with the second taking place four to six weeks before slaughter. After the second dose, the boar's testicles stop growing. The handler should be trained in the use of the vaccine and the vaccinator with enhanced safety features.
The vaccine is claimed to offer an animal-friendly and a more environmentally sustainable solution to boar taint, it and to allow stakeholders across the pork production chain to reap the performance benefits of natural boar growth while preserving eating quality. However concerns about the effect of the drugs on animal and consumer health have been expressed.
The vaccine can have serious side effects if accidentally administered to human including temporary and permanent sterilization. According to an EU report:“Accidental self- injection may produce similar effects in people to those seen in pigs. The risk of these effects is greater after a second or subsequent accidental injection than after a first injection.“ The manufacturer's web site further expands on this: “accidental self-injection may produce similar effects in people to those seen in pigs. These may include a temporary reduction in sexual hormones and reproductive functions in both men and women and an adverse effect on pregnancy. The risk of these effects will be greater after a second or subsequent accidental injection than after a first injection. The product label advises anyone who has received an accidental self-injection to seek medical attention immediately and not to use the product in the future.“
- Bonneau M, et al "Contributions of fat androstenone and skatole to boar taint Sensory attributes of fat and pork meat" Livestock Prod Sci 1992;32:63–80
- "Boar Taint"
- Researcher Douglas L. Greger, PhD, Research Director, Templar Research and Development & Farmer W. Jeffries. "Piglet Interventions". Sugar Mountain Farm Personal eMail Communications.
- Dunshea FR, et al "Vaccination of boars with a GnRH vaccine (IMPROVAC) which is claimed to eliminate boar taint and increases growth performance" J Anim Sci 2001;79:2524–2535
- Jeong J, et al "The effects of immunocastration on meat quality and sensory properties of pork loins", in Proceedings 20th Int Pig Vet Soc Cong, Durban, South Africa, 2008
- Singayan-Fajardo J, et al. "Eating quality and acceptability of pork from IMPROVAC immunized boars." In Proceedings 19th Int Pig Vet Soc Cong, Copenhagen, Denmark, 2006
- Jeong J, et al. "The effects of immunocastration on meat quality and sensory properties of pork bellies." In Proceedings 20th Int Pig Vet Soc Cong, Durban, South Africa, 2008
- Giffin B, et al. "Consumer acceptance of the use of vaccination to control boar taint is poor as it is adding one more chemical to the meat." In Proceedings 20th Int Pig Vet Soc Cong, Durban, South Africa, 2008
- Hennessy D, Newbold R. "Consumer attitudes to boar taint and immunocastration: A qualitative study." In Proceedings 18th Int Pig Vet Soc, Hamburg, Germany, 2004
- Hennessy D. "Consumer attitudes to boar taint and immunocastration." In Proceedings 3rd Asian Pig Vet Soc Cong, Wuhan, China, 2007
- Allison J. "IMPROVAC: Consumer acceptance." In Proceedings Pfizer Symposium at 20th Int Pig Vet Soc Cong, Durban, South Africa, 2008
- Lagerkvist AJ, et al. "Swedish consumer preferences for animal welfare and biotech: A choice experiment." AgBioForum 2006;9(1):51–58
- Juliette Jowit "Fears over use of chemicals to castrate pigs" The Observer, Sunday 24 January 2010
- "GONADOTROPIN RELEASING FACTOR (GNRF) ANALOGUE-PROTEIN CONJUGATE" (PDF).
- "Pfizer FAQ".