Texas Tech University

Pig Castration

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Over 100 million pigs are marketing in the USA each year. With half of these animals being males, we understand that over 50 million male pigs are sent to market. In the USA virtually all males are physically castrated at a young age (predominantly) with no anesthesia or analgesia (pain relief).

The market weights of pigs are 260-300 lb today. Onset of puberty varies with genetic line, but most males pigs enter puberty in the 220 to 240 lb range (now about 5 months of age).

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About Boar Taint

When male pigs develop sexually (puberty), they develop a natural pheromone and gut product that smell offensive to many people. The pheromone (Androstenone) and an intestinal product (Skatole) give the meat from adult, male pigs and this offensive odor. Boar taint smells like old gym socks or bad human body odor. Some people say the pig and the human share some related offensive steroid odors. This off odor is called “Boar Taint.” Boar taint is largely prevented by physical castration. However, castration is painful. Many consumers who experience Boar Taint are put off eating pork.

  • This odor occurs mainly, but not exclusively, in mature intact male pigs. Depending on age, breed and environment, 50 percent or more of all intact male pigs produce pork that has a strong to moderate off-odor when cooked.
  • While these odors do not represent a food safety concern, they need to be controlled to ensure a high-quality eating experience.
  • Boar taint is prohibited by food quality regulations in most countries.

Percentage of intact males exhibiting off-odor compounds.


In research from the European Union, more than 25% of intact males exhibited off-odor compounds, with androstenone and/or skatole in fat tissue above sensory thresholds (Figure on the left).

Why Unpleasant Aromas Occur

As male pigs approach puberty, they begin developing two naturally occurring compounds that can cause an unpleasant aroma in cooked pork. This off odor is technically referred to as "boar taint." These natural off odors create no food safety issue, but need to be controlled to protect the quality experience of eating pork.

  • The two compounds are androstenone and skatole. They can accumulate in the fatty tissue of male pigs, and are released when the pork is cooked causing the unpleasant aroma.
  • Depending on age, breed and environment, as many as 50% or more of all intact male pigs produce pork that has a strong to moderate off odor when cooked.

The Biology Of Off Odors


Two compounds, androstenone and skatole, occur naturally in male pigs as they mature. If not controlled, they can create off odors in cooked pork. Androstenone acts as a pheromone in the boar as it is released in the saliva and other fluids.

Economic forces drive the slaughter weights higher – it takes about the same labor to process a 300 lb pig as a 220 lb pig – so labor costs per pig decrease with higher slaughter weights. If pigs were marketed at, say 200 lb as the do in Britain, then the males would not have to be castrated. But with market weights in the USA much higher, castration is required to prevent Boar Taint.

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Why call it “Physical” Castration?

Castration of the male pig refers to removal of the testes. This is usually done with a non-sterile knife or scalpel and in the barn (not a surgical suite). The procedure is performed rapidly and it may be performed on a large number of animals in a given day by skilled animal technicians. The procedure is described below.

The routine castration of pigs is not performed with pain relief, nor is it performed in a sterile field using sterile instruments. Castration is performed in a commercial production unit. Typical castration cannot be considered a surgical procedure. But it is a physical method of removing the testes.

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How is Castration Performed?

pig castration

Castration is performed by first restraining a young piglet in some manner. Some people sit in a chair and put the piglet's body between their legs (see photo). Then, a scalpel (or knife) cuts the skin on the scrotum. Then the person pulls the testes away from the body. They may cut the spermatic cord or sever it with the scalpel using a serrating motion. Then the open wound is typically sprayed with a disinfectant such as iodine.

The pig experiences pain and distress associated with: handling, cutting the scrotum and spermatic cords, and post-surgical pain associated with healing. The post-procedure pain lasts 2 hours or so in piglets and longer in older males.

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The Science of the Pain of Castration

The first scientific paper on the pain of castration was published in 1988. In this work, McGlone and Hellman castrated piglets (3 days old) or nursery-age pigs (7 weeks old) with and without local or general anesthesia. The authors measured behavior, growth and mortality.

McGlone, J. J. and J. M. Hellman. 1988. Local and general anesthetic effects on behavior and performance of 2 and 7 week old castrated and non-castrated piglets. J. Animal Science. 66:3049-3058.

Presented in Figure 1 is a summary of the effects of local anesthesia on nursing behavior in piglets. Castration reduced nursing behavior. This effect was partially reversed by use of local anesthetic. This is evidence that castration is painful during this 3-hour period after castration.


Local anesthesia relieves the procedural pain but when it wears off in about 30 to 60 minutes the pain returns. Several studies have been published on use of different anesthetic agents (to remove procedure pain) and analgesics (to attempt to remove post-procedure pain). Effective analgesics have not been identified at this time.

Local anesthetics are effective if pigs are handled to administer the drug (which is stressful) and then the handler must wait for the local to take effect. Then the pigs are handled again (another stress) and the procedure performed (with less pain). This double handling and the stress of injecting local anesthetic into the testes and scrotum make this option less than desirable.

General anesthetics are effective, but in very young piglets, general anesthetics can be poorly tolerated. Piglets can die from general anesthetics that are otherwise safe for adult pigs.

In addition to the above issues with anesthetics, none are approved for use in food animals in the USA. IF the FDA or USDA were to find residues of unapproved drugs in pigs, this would not be good for the producer or the industry, let alone consumers.

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Alternatives to Physical Castration

For each potential alternative to Physical Castration below, you can click on the link for more information. Alternatives include:

  • Market at a younger age (before puberty)
  • Use pain relief – local or general anesthetics
  • Genetic selection against Boar Taint
  • Immuno castration (also known as immunological control) (White Paper - June, 2012)
  • Improvest

At this time, marketing pigs at a younger age is not economically feasible in the USA. Pain relief drugs are not currently approved for use in pigs by the FDA. Genetic lines of pigs with low Boar Taint are not currently available (but may be under development). One immuno castration product is approved for pigs (Improvest by Pfizer Animal Health).

The immuno castration approach uses the pig's own immune system to control the substances that cause off odors. It's a protein compound that works like an immunization.

Immuno castration is approved in 60 other countries around the world, including the European Union, Australia and Japan, under the brand names IMPROVAC and IMPROVEST. IMPROVAC has been used successfully by farmers in some countries for more than 10 years.

Improvest is an FDA-approved immuno castration product that reduces boar taint. IMPROVEST is not a hormone or growth promotant. It's not added to the feed or genetically modified. And, it is not chemical castration. It's a protein compound that creates a temporary immune response to manage the unpleasant aromas.

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What do Activists and the Industry say about Castration?

Activist views

Activists are critical of castration of pigs because it involves a painful procedure and pain relief is not given. Often activists blend in sow housing, castration and tail docking. You can see data and information on sow housing on our web site. We have done work on tail docking and will write about that later; basically, there are better methods to tail dock, and analgesics available. We focus here on the issue of castration.

Examples (among many) of activists' positions are found here:

Mercy for animals says they documented: “workers ripping out the testicles of conscious piglets with the use of painkillers”

In April of 2012, HSUS filed a legal complaint against the National Pork Producers Council stating, among other claims that: “…what producers call baby-pig processing and HSUS calls mutilations-- tail docking, castration, needle-teeth clipping—that “these abusive practices allowed by the We Care and PQA Plus programs are fundamentally inconsistent with NPPC's public claims.” HSUS points to its undercover videos as documenting practices that most consumers do not consider humane.”

The objective information provided by activists is clouded by sensationalism (ex., “ripping out the testes”). Painkillers, while a good idea, have not been shown to be effective for this type of pain and most are not approved for use in food animals by the FDA.

Industry views

The industry states, correctly, that male pigs are castrated primarily to prevent boar taint.

The above video makes three key points. They say that the swelling is minimal. They say that “they go back to a natural behavior rather quickly.” They say that the pain is there, but “we can't really measure it” (these are not the case; see McGlone and Hellman, 1988; McGlone et al., 1993 and Sutherland et al., 2010; (two of which were funded by the industry). Marketing intact males as a young age (before boar taint develops, as is done in the UK), immunological castration (available now) and genetic selection against boar taint (possibly in the future) were not mentioned by this video.

The Science

The truth is that the science is there to say (a) castration hurts, (b) pain killers are not available nor totally effective, and (c) alternatives are available. The purpose of this information is not to be an advocate for any particular way forward, but to provide objective science-based information.

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General Philosophy about Castration as an Animal Welfare Issue

The hottest Animal Welfare topic at this time in the USA pig industry is Gestation Sow Housing. The welfare of pregnant pigs is similar, all things considered, when the sows are in crates as it is when they are in pens. But public perception, and perhaps the ethical view of some people, are forcing change. Some states have banned the use of gestation crates. Sow housing is a case where a marginal animal welfare issue (in my view) is causing industry change. Pig physical castration is a real animal welfare issue – to the pig. And few people argue that the pig is not suffering when castrated in the present USA situation.

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Scientific Publications

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Private Site for Collaborators

FASS held a webinar on the Science of Swine Castration on October 8, 2012. The recorded webinar can be found at: http://www.fass.org/2012AnimalCareSeries/SwineCastration/recordings.asp

For questions or comments, please email Dr. John J. McGlone


Laboratory of Animal Behavior, Physiology and Welfare