Immunological castration proven to reduce boar taint in market hogs

2011-10-27T09:00:00Z Immunological castration proven to reduce boar taint in market hogsBY JEFFREY HOFFELT, LIVESTOCK EDITOR Agri-View
October 27, 2011 9:00 am  • 

First in a series

Traditional castration methods have been perfected on swine operations for decades. Though surgically castrating boars efficiently prevents boar taint at market time, barrows typically require additional nutrients and provide lighter-muscled carcasses. A new technology is becoming available so that producers can avoid surgical castration-reaping the growth benefits of boar systems while still avoiding boar taint.

Known as immunological castration, a new vaccine patented by Pfizer can be given to boars close to slaughter as a substitute for castration. A double injection of the vaccine works to turn off testosterone and prevent boar taint in meat.

In the United States, the marketable product is known as Improvest. It was approved by the Food and Drug Administration (FDA) as a prescription product in March and is expected to become widely available in the near future.

Steven Dritz, DVM, Ph.D., is a professor of animal science at the College of Veterinary Medicine at Kansas State University. Along with conducting a number of field trials at the Midwest school, he also worked with the FDA and the U.S. Department of Agriculture (USDA) in their evaluation of the product.

"This is a technology that was developed in Australia about 15-20 years ago. It's been commercialized in the U.S. and in about 50 countries around the world right now," he says, explaining that Pfizer currently has a five year exclusive patent on the product and is now creating it on a limited scale for commercial production.

Dritz defines immunological castration as using the immune system to suppress testicular function as an alternative to surgical castration done early in life. Because boars have been proven to yield stronger carcasses and grow quicker, the tool allows hogs to grow as boars for most of their lives. The vaccine can be given before slaughter to prevent testosterone levels from entering the meat-ultimately, preventing boar taint in the marketable product.


The vaccine works by inducting antibodies to endogenous Gonadotropin-releasing hormone (GnRF) which temporarily blocks pituitary-gonadal endocrine axis. In short, Dritz explains that the vaccine triggers antibodies in the boar and tells the brain to turn off communication to the testicles.

"After two injections, the animal begins acting like a barrow from an endocrine and hormonal profile," he says.

Because boars are more feed efficient and have a higher lean meat yield compared to barrows, immunological castration works to allow the hogs to utilize those characteristics.

"Immunological castrated male pigs spend a large proportion of their lives as boars," Dritz says. "However, immunological castration temporarily blocks production of sexual hormones that are the cause of boar taint."

According to the researcher, the biggest advantage to the producer is that boars are more feed efficient.

"They're leaner so depositing less fat takes less energy and we can improve feed utilization," he says. "The idea is that the pigs spend a large proportion of their growing lives as boars and then you can castrate them just prior to market. When you send them to market, the boar taint is then reduced because you blocked those sexual hormones."

To achieve the benefits of boar growth and barrow carcass qualities, the immunological castration technology must be subcutaneously injected into the boars twice before slaughter.

From his studies, Dritz has found that the first vaccine should be given between days 119 and 133. That injection primes the immune system while retaining full testicular and reproductive function.

"The pigs don't even respond to this and there is no detectable antibody in the Improvest animals," he says. "This injection works to set up the immune system for the second injection."

The second injection is then given to the boars around day 154 of feeding.

"Within a week after the second injection, there's a high amount of antibodies circulating in the bloodstream of that pig," Dritz explains. "A dramatic immune response is obvious. The second injection induces a strong immune response that causes temporary suppression of testicular function. It doesn't have any negative affect on where the GnRF is produced in the pituitary-it's just like a roadblock in the bloodstream."

To avoid boar taint, hogs that have been immunocastrated must be marketed between four and eight weeks after they are given the second injection.

Dritz says the short marketing window is essential in avoiding withdrawal times and preventing testosterone actions from recurring.

"As we move away from the time of that second injection, those antibodies (that halted communication between the brain and the testicles) are beginning to decrease," he says. "Eventually they will fall to a point where testicular function will be stimulated again. If you keep the pigs around long enough, that function will return."

Current studies show that the effects of the vaccine last for approximately 12-16 weeks following the second injection.


When implemented properly, the immunological castrating system works to eliminate circulating testosterone that is responsible for the development of the sexual characteristics of the male.

"By blocking that testosterone production, you're reducing the whole sequence of the metabolic functions that produce boar taint," Dritz says. "Boar taint comes from metabolites or sequential compounds of that testosterone production."

Focus groups created by the FDA during the testing process evaluated meat from the immunocastrated hogs to determine if boar taint was avoided with Improvest. The consumers experienced a one-third reduction in boar tainted pork from hogs harvested more than four weeks after the second vaccine. A 50 percent increase in aroma and flavor was experienced in hogs harvested six weeks after the second injection.

FDA's evaluation of the product also compared the serum testosterone levels in immunocastrates compared to barrows and boars by measuring the amount of testosterone in the bloodstream of the pig.

"Prior to the first injection and prior to the second injection, the immunological injected animals and the boars have very similar testosterone concentrations that were dramatically higher than the barrows," Dritz says. "Then, as we give the second injection and the boars are maturing and reaching sexual puberty, their testosterone production is starting to dramatically increase; whereas the vaccinated boars have dramatically decreased in testosterone production."

The agency's records of decreased levels of testosterone in the immunocastrated hogs led them to examine the marketable meat scientifically based on a visual analog scale. With scores ranging from 0-150, the meat was tested for signs of boar taint. The final scores given to a test group of carcasses were: barrows 2.7; boars 45; and immunocastrated hogs 5.2.

"Improvest treated pigs and barrow animals were similar on the visual analog scale while boars were dramatically higher," Dritz says. "There is definitely a clear improvement with the immunological castration in visual scores of boar taint."


Currently, Improvest is not widely available on the commercial market but it can be purchased as a prescription drug through veterinarians in some locations.

"The product is only available through veterinarians due to the precautions for human safety," Dritz says. "It must be given with a special safety injector, because accidental self-injection can interfere with reproductive function in both men and women."

Because proper training and safety considerations for administration are critical, Pfizer is expected to conduct certification training as the product gains more steam.

With growing interest in the product, some packing plants are requesting that swine producers who use the product keep records on vaccination dates and levels. Similar verification is needed by USDA-inspected slaughter plants, Dritz says.

"There are several clear benefits to utilizing immunological castration over surgical options, so this is a topic that we're probably going to be hearing more about," he adds. "Vaccine availability will ramp up as the production facilities come online."

Editor's note: Dritz and his colleagues at Kansas State University have found that immunological castration can have a significant effect on the amount of lysine required during swine feeding. Watch for more on that study as this series continues.

Copyright 2015 Agri-View. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.

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