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This site provides technical and program information for veterinarians and farmers. If you are a consumer looking for general information, please visit the IMPROVEST®(gonadotropin releasing factor analogdiphtheria toxoid conjugate)Consumer Resource Center.


IMPROVEST® is a veterinary prescription product that is a safe and effective alternative to physical castration. It’s a protein compound that works like an immunization to protect against unpleasant aromas that can occur when cooking pork from some male pigs.

FDA-approved, IMPROVEST® is for the temporary immunological castration and reduction of boar taint in intact male pigs intended for pork. It uses the pig’s own immune system to provide the same effect as physical castration, but much later in the male pig’s life.


IMPROVEST® works like an immunization, using the male pig’s immune system to temporarily reduce the two major off-odor causing compounds in pork, androstenone and skatole.

The Pulpit Rock
Figure 1

IMPROVEST® is given subcutaneously behind the base of the pig’s ear in two 2-mL doses that:

  • Primes the immune system. The first dose primes the pig’s immune system, but does not create any physiological change in the pig. This dose is given no earlier than nine weeks of age.
  • Stimulates an immune response. The second dose creates the effective immune response (Figure 1). It is given a minimum of four weeks after the priming dose, and also is timed for administration between three to 10 weeks before the pigs go to market. This dose stimulates the immune system to produce specific antibodies that prevent the biological cascade that controls testicular function and results in temporary immunological castration.
  • Decreases off-odor compounds. Following the second administration of IMPROVEST®, androstenone and skatole levels drop and remain suppressed for at least eight weeks. Sexual and aggressive behaviors also decline. Animals behave more like barrows. 1,2

Pigs should not be sent to market prior to three weeks after the second dose to allow adequate time for reduction in the compounds responsible for boar taint. Marketing pigs given IMPROVEST® more than 10 weeks after the second dose may increase the risk of off odor in pork. IMPROVEST® should not be used with female pigs, barrows or male pigs intended for breeding.


Capture More Value By Growing Intact Males

Male pigs are given IMPROVEST® later in the finishing phase to manage off odors, eliminating the need for physical castration. As a result, they’re able to grow to their full intact male potential, with all the inherent advantages, until the second dose. Advantages documented in global studies include:

  • Improved feed efficiency 3
  • Increased cutout yield 4
  • Reduced piglet mortality 5
  • Decreased carbon footprint 6

With the need to feed a growing world population, this approach has the potential for greater protein production with the use of fewer resources.

Safe, Quality Meat

Pigs raised using IMPROVEST® produce the same high quality pork (free from unpleasant odors) consumers enjoy today.1 The U.S. Food and Drug Administration has determined that meat from pigs given IMPROVEST® is safe to eat. Regulatory authorities in more than 60 other countries, including the European Union and Japan, have reached the same conclusion for the related global brand IMPROVAC.


IMPROVEST® is Effective at Managing Off-Odors

Research in the United States and around the world has shown that this technology is as effective as physical castration at reducing the male-related off odors in pork. 1

In large U.S. multi-site IMPROVEST® sensory studies, consumers who represented the general population with an innate ability to detect aroma and flavor associated with boar taint were asked to evaluate pork from intact males, physically castrated males and male pigs given IMPROVEST®. The research concluded that consumers could not differentiate between pork from pigs given IMPROVEST® and physically castrated pigs. 1 On the other hand, they could detect an aroma and flavor difference in the pork from intact males vs. those given IMPROVEST®.

Another way to look at the effectiveness of a product is by evaluating the levels at which the two primary off-odor causing compounds (androstenone and skatole) can be found in the fat tissue of the pork. Accepted sensory threshold values indicate the levels at which a person who is sensitive to the off-odor compounds may detect them. Accepted sensory thresholds for androstenone is at or below 1.0 μg/g and for skatole it is at or below 0.20 μg/g. 1

Figure 2

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 2).1

Figure 3

After administering IMPROVAC (related global brand) in 578 intact males, levels of off-odor compounds fell below the sensory threshold in nearly 100% of male pigs,1 with only three low level incidences of skatole (Figure 3). Elevated skatole levels can also be the result of diet or environmental conditions.


Approved as safe and effective in 64 countries,
including the European Union and Japan, China, South Korea, Russia and other countries through its related brands, IMPROVAC® INNOSURE® and VIVAX®

No residues in the meat from
IMPROVEST® that could affect human health1

Zero day withdrawal

Used for more than 10 years in some parts of the world

Export: No restrictions

No food labeling required

1- Freedom of the Information Summary. IMPROVEST® (gonadotropin releasing factor analog - diphtheria toxoid conjugate). NADA 141-322.


Verified quality assurance process

With IMPROVEST® you get more than just a product, you get a program. Zoetis will work with you to implement the verified process to ensure the program's comprehensive quality assurance protocols are met. This support can be in the form of Zoetis employee technicians, who are trained and certified to administer the product, or Zoetis will train and certify your staff to administer IMPROVEST®.

The IMPROVEST® quality assurance program includes:

  • Available only through a veterinarian’s prescription.
  • Proprietary tracking system records prescriptions, training, two-dose timing and in-barn quality assurance inspections. This provides accurate documentation to certify barns of pigs have met program requirements.
  • The first tracking system software for animal health production in the world.

  • Only trained, certified personnel can administer IMPROVEST®.


Certified, verified quality assurance process

Use of IMPROVEST® requires change and coordination throughout the pork value chain.

First, it means growing intact males, which brings new management considerations. Intact males have different nutritional requirements because they are more efficient at converting feed to meat.

As the product is introduced, Zoetis will work with veterinarians and their producer clients to help them adopt new nutritional guidelines and best handling practices to optimize growth for intact males. Product availability will increase gradually as the experience of working with intact males expands. IMPROVEST® is size-neutral. It can be used on, and has benefits for, any size farm.

Second, this gradual approach also provides the time needed to ensure a coordinated food chain effort and gives packers and processors time to integrate and optimize this into their systems, as well.

The goal is to have the best IMPROVEST® program experience for everyone – from producers to meat packers and processors, retailers and, ultimately, to consumers.