Castrating male pigs can be a controversial issue. Certainly the animal  activists like to feature the practice as one that causes stress and pain to piglets. While they argue that anesthesia should be used, the reality is that such application on the farm is impractical and options are limited.

Producers have long thought about tapping into the performance benefits of keeping male pigs intact. However, the risk of boar taint tied to meat products and the potential consumer backlash have been too high a price to pay.  

More than 60 countries have approved immune-castration techniques and no longer castrate boars. Of course, many of those countries market hogs at lighter weights and earlier maturities than in the United States — a challenge, but not an insurmountable one.

In fact, this year the U.S. Food and Drug Administration approved immune castration for use in the United States, which may expand your production options in the future.

The unique immune-castration product, Improvest (gonadotropin releasing factor analog-diphtheria toxoid conjugate), comes to the U.S. market from Pfizer Animal Health. The veterinary-prescription product uses a series of two injections, triggering the boar’s immune system to temporarily reduce androstenone and skatole — the two major compounds that cause off-odor in pork. It reduces the impact of puberty and allows you to leave boars intact throughout the growth period.

“This is a new class of product —biopharmaceutical,” notes Jim Bradford, DVM, Pfizer Animal Health. In the European Union and Japan, the global brand for immune castration is Improvac. That product has been used in some countries for more than 10 years. “What we have learned from experience there has helped with the product here,” he adds.

E.U. regulatory authorities declare that meat from pigs receiving Improvac “would not contain any potentially harmful residues” and that the consumption of pork from these pigs “poses no risk to the consumer.” FDA agrees and has determined that meat from pigs given the Improvest product is safe to eat.

With feed prices nearing all-time highs, everyone is looking for opportunities to increase performance.  “Improvest creates an opportunity to capture more value from male pigs,” Bradford says. “Male pigs are given Improvest later in the finishing phase to manage boar taint, so they’re able to grow to their full, intact male potential, and do it more efficiently.”

“Immune castration is something we are going to hear much more about in the future,” says Steve Dritz, DVM, a swine specialist with Kansas State University. “The product produces antibodies against the communication circuit between the brain and the pig’s testicles. This makes the animal basically behave like a barrow from a hormonal profile.”

What are the advantages? “Boars are more feed-efficient and develop less fat deposits throughout the growth phase,” Dritz says. “Immune-castrated male pigs spend a large proportion of their lives as boars.”

Dritz and his Kansas State colleagues tested the product to determine the effect on growth performance and carcass characteristics involving different lysine levels in the diets of barrows, untreated boars and male pigs receiving Improvest. The performance data for the research trial were recorded between day 55 (after weaning) through day 160, and involved six animal test groups. They were: barrows, low lysine; Improvest, low lysine; Improvest, medium-low lysine; Improvest, medium-high lysine; Improvest, high lysine; boars, high lysine. The dietary lysine levels varied from 1.04 percent to 1.31 percent at the start of the trial period and were subsequently reduced over four feeding phases. (To review the lysine levels used in the trial, go to

In addition, Dritz measured performance parameters of the treatment groups, including feed efficiency, relative to barrows. (See the accompanying table.)

“A key point of understanding the product is looking at feed efficiency during the time period after the second injection, or day 122 through day 160,” Dritz says. “During that period we get a nice improvement in feed efficiency in the pigs receiving Improvest. After the second injection, pigs fed the low and medium-low lysine diets grew faster than barrows and boars, with similar feed efficiency as boars.”

“It’s important that for part of their lifespan these pigs are fed like a boar,” Bradford says. “After the second injection, they should be fed like a barrow.” He points to data that shows the feed efficiency advantage at 6 percent to 10 percent for pigs receiving Improvest.

Dritz recorded carcass weights in the trial and found that immune-castrated pigs receiving the low or medium-low levels of lysine yielded a significant increase in carcass weights.

Also included in the trial was income over feed cost of the treatment groups. While margins will vary with feed prices, the Improvest-treated pigs receiving medium-low and medium-high lysine diets averaged $5 per pig in income over feed cost. “This assumes the same carcass price for barrows and pigs receiving Improvest, and does not include cost of the product or cost of injections,” Dritz says.

Trials measuring the use of ractopamine in immune-castrated pigs have been conducted in Australia. “That data shows an additive effect provided by ractopamine,” Dritz notes. “Of course, when you feed ractopamine, you would have to make appropriate diet adjustments.”

No objections to use of the product have surfaced in export markets, which is an increasingly important consideration for U.S. pork producers. According to the U.S. Meat Export Federation Export Services team, “We are not aware of any objections to the use of Improvest — or its related global brand, Improvac.”

At home, Pfizer has presented the product information and related performance data to packers. “They are interested and cautious at the same time,” Bradford says. “For a time, I  expect packers to run their own trials.”

The advantages of immune castration are many. Managing the injection process however, will take more study and practice.  But these days, any advantage in pig performance is worth investigating.

Transparency and Training Required

Improvest is the first product available in its class (immune castration) in the United States and Pfizer Animal Health has a five-year exclusivity. The company is launching the product in a phased approach because it wants to audit the process and ensure that Improvest is being used properly and effectively.

“We’re not selling a product in a bottle; this is one of the most partnering projects I’ve ever been involved with,” says Jim Bradford, DVM, Pfizer Animal Health.

It’s important that injection crews are thoroughly trained in the product’s application, Bradford says. In fact, Pfizer has an extensive training program, involving a web-based session which runs about 3 hours. This is followed by on-site training where crews are supervised for up to a week, and a quality assurance manager must sign off on the completed training.

“These people are important to the process,” Bradford adds. “They need to be stable and detail oriented.” He recommends keeping this in mind when producers are screening for injection crew candidates. For example, product and needle use must be counted and accounted for per each pig group. 

The immune-castration process involves two subcutaneous, 2-ml injections behind the base of the male pig’s ear. The first dose primes the boar’s immune system and should be administered no earlier than 9 weeks of age. The second dose should be administered at least four weeks later.

Actual injection of the product is done via a specially designed syringe, which includes a safety shield over the needle and has to be purposely activated. “The injection direction is always away from you,” Bradford notes, to avoid accidental self-injection during administration. Accidental injection could negatively affect reproductive physiology of both men and women.

Pigs should not be marketed until at least four weeks after the second dose but not later than eight weeks. “You have a four- to eight-week window of suppression where you can market the pigs,” Bradford points out. This allows adequate time to reduce the compounds responsible for boar taint.

  A certificate will be generated with information regarding the pigs’ immune-castration status for the packer. It can accompany the trucker or the packer can pick it up on the Internet. “USDA says if the pigs arrive with the certificate, they are barrows,” Bradford says. “The process is just like for USDA Verified Production.”

Immune castration offers another option to producers and could temper animal-welfare critics. “It’s animal friendly and continues to provide consumers safe, affordable, wholesome pork,” Bradford notes.