Branded as Improvest in the United States, the generic name for the active ingredient is gonadotropin releasing factor analog-diphtheria toxoid conjugate. Its mode of action is to temporarily and immunologically block gonadotropin releasing factor (GnRF), which reduces the levels of androstenone and skatole in mature male pigs — the primary source of “off odors” in pork.

Androstenone and skatole occur naturally in male pigs as they reach puberty at 4 to 6 months of age. This off odor is often referred to as “boar taint.” Castration of male pigs at an early age prevents them from reaching sexual puberty, thus eliminating the source of off odors.

Improvest was approved by the U.S. Food & Drug Administration (FDA) in 2011. Regulatory authorities in more than 60 other countries, including the European Union and Japan have also approved its use. Labeled as Improvac in some countries, it has been in use for over 10 years.

Shelley Stanford, DVM, Pfizer technical services director, positions the product as an alternative way to capture the value of intact male pigs while also managing the occasional issue of off odors in pork.

“Improvest is elegant in its simplicity,” she explains. “It is a protein compound that works like an immunization. It uses the pig’s own immune system to temporarily provide the same effect as physical castration to manage the substances that can cause unpleasant odor in pork from male pigs. It is administered later in life, which allows these pigs to grow as intact males, capturing the inherent value and efficiencies of growing intact males.”

Explaining the generic name further, Stanford breaks it down like this:

  • Gonadotropin releasing factor (GnRF) is a compound that all animals produce naturally as they mature. Improvest does not contain naturally occurring GnRF, but rather contains an incomplete version of it (analog), which makes it inactive.
  • Diphtheria toxoid (DT) is the same as the standard diphtheria vaccine that has been safely used in global childhood vaccination programs since the 1930s. It is a protein that contains natural amino acids. It is used as the carrier (conjugate) protein for the incomplete GnRF analog molecule.
  • Conjugate means to join together. Two compounds need to be conjugated to produce the immunological response in the pig. Together, the compounds act as an immunization to control the substances that create off odors.

Stanford feels it is particularly important for consumers to understand what Improvest is not. It is not a hormone. It is not chemical castration, which would potentially imply a direct injection into the testicle. It is not genetically modified or permanent. It is not in and of itself a feed additive or a growth promotant. Rather, the growth rate and feed efficiency improvements commonly seen with the use of the product are the result of allowing intact males to grow naturally until later in life, when the product is administered.

“There are no residues in the meat from Improvest-managed pigs that could affect human health,” Stanford explains. There are no export restrictions on the meat from Improvest -managed male pigs, and the product has no withdrawal.

While Improvest has been cleared for use, the company has been working with university researchers and swine veterinarians in the United States to gather more scientific and field data before formally rolling it out to the broader industry during a mid-December Pork Chain Summit in Miami, FL.

Understanding Boar Taint

Setting the stage, swine behavior specialist John McGlone, Texas Tech University, provides a brief overview of boar taint and the reasons young male pigs are castrated to manage the off odors caused by androstenone and skatole.

As the complete pig genome has unfolded in recent years, much has been learned about the pig’s ability to smell and taste, he begins.

“The pig is unique in that it has more olfactory — sense of smell — genes than most other species. It can smell more things than people can smell and they can smell them at lower concentrations. In fact, the pig’s olfactory capabilities are about 40,000 times more sensitive than a human’s,” he says.

While their ability to smell is acute, their sense of taste has fewer genes than humans. “They can find all kinds of smelly things to eat, but they don’t care what it tastes like,” McGlone says.

In the wild, pigs became scavengers and opportunistic feeders — consuming most anything they could find. These feral ancestors developed matriarchal pig societies where the mature females were clearly in charge.  Boars were loaners, allowed into the group only when the females were in heat. That’s where the sense of smell became very important.

As pigs evolved, successful boars produced more of the pheromone androstenone in their saliva. “The saliva advertises a boar’s ‘boarness’ by releasing these stinky steroids into the air to attract the female. The sows select the smelliest boar around,” he continues.

The first pheromone discovered in mammals was the discovery of androstenone in pigs in 1968, primarily because it was present in such high concentrations in the saliva and the fat of male pigs, McGlone notes. Skatole, produced in the lower gut, is also taken up in the blood and fat and remains there in intact male pigs. In gilts and barrows this compound is cleared efficiently by the liver, while in intact males the efficiency of liver clearance is reduced by testicular steroids.

As a means to eliminate this innate ability of male pigs to produce pheromones when they reach sexual maturity, hog farmers castrate the young males.

Odor of the Beholder

Sensitivity to boar taint in pork varies in people. According to a recent meat science study, about 43% of women and 53% of men cannot smell androstenone. However, about 20% of people are highly sensitive to the pheromone and 28% have medium sensitivity.

“The first thing to remember about boar taint and the androstenone pheromone is that people in the United States do not know this story; they do not know about boar taint and that it smells bad. Nor do many people know that pigs are castrated or why they are castrated,” McGlone continues.

Still, the fact remains that literally half of the pigs born in the United States have the innate potential to develop off odors when grown beyond their sexual maturity (over 220 lb.). The options available to eliminate the off-putting odor are castration, genetic selection (slow and expensive), semen sexing (cost prohibitive), developing methods to block pheromone-producing capabilities and, now, immunological castration.

The Improvest Program

Use of the product requires a veterinary prescription to ensure proper handling, administration and tracking. “Everything that happens with these Improvest pigs is tracked,” Pfizer’s Stanford assures. Everyone who administers the product must complete a three-step training program:

Level 1 — Web-based, audio-visual training.

Level 2 — Introduction to the product and training in biosecurity protocols, care and use of specially made injection equipment, administration techniques, professional behavior and worker safety with the product and with the animals.

Level 3 — Quality assurance training to ensure technicians are competent to administer Improvest and utilize the tracking program, Improvest Platform with Global VetLink. Veterinarians can serve as quality assurance administrators and provide training.

The first injection, given at 9 weeks of age or older, simply primes the pig’s immune system. The second dose is given at least four weeks after the priming dose.

Two weeks after the second dose, a quality assurance inspection takes place. Pigs are checked closely to identify “suspect” animals — those exhibiting boar-like behavior such as mounting penmates. “This is critical to the program,” Stanford emphasizes.

The quality assurance inspector records key information into a SmartPhone, such as training certification, the number of vials and doses prescribed and used and key production data (i.e., growth rate, pen or barn feed efficiency). The program is linked to a GPS to track pig location and movement. “Very critically, a certificate accompanies pigs to market, which links to the Improvest Platform and assures packers that these are barrows,” she says.

“We have taken a gradual, thoughtful approach to introducing this product to the market. First, we wanted to ensure that ‘best practices’ were in place, including nutritional guidelines, best handling practices, animal care and management guidelines. We’re raising intact males now and we want to capitalize on all of the efficiencies associated with that. We also wanted to ensure a coordinated food chain effort — giving packer-processors time to integrate these intact males into their systems,” Stanford explains.

Carcass Quality Traits

Much of the carcass quality work pertaining to Improvest was conducted at the University of Illinois. Former Illinois graduate student Dustin Boler, now at Ohio State University, provided an overview of pork quality attributes of immunologically castrated (IC) barrows.

“At a similar age, live weight of IC barrows is greater than physically castrated (PC) barrows,” he begins. “The presence of the testicles accounts for about 0.3% of carcass yield, plus we have an increase in visceral weight (other reproductive tract components, liver, kidneys) and intestinal mass/gut fill, which decreases carcass yield of IC barrows by about 1.12 to 1.87%. But overall, IC barrows are about 8% more efficient in converting feed to lean, and their average daily gain is about 4.2% better,” he says.

Boler analyzed a composite list (seven to nine research reports) that identified four key pork quality parameters that are important whenever a new technology is considered:

Pork quality: “Often, when we talk about meat quality, the discussion begins and ends with color because it is the number one driver of a consumer’s intent to purchase,” he says. No lean color differences were noted in IC vs. PC barrow carcasses.

Next in the quality discussion is tenderness, measured objectively by Warner-Bratzler shear force, which simulates the amount of force required to chew through a piece of meat. Subjective estimates of tenderness were also conducted with trained and untrained panels. “Tenderness drives repeat customer purchases,” Boler says. No difference in tenderness was found.

“Muscle is about 75% water, so water-holding capacity (WHC)/drip loss is very important to its ability to retain water,” he explains. No WHC differences were found.

“One of the most important measures of meat quality is pH because it most closely influences the other meat quality parameters,” Boler points out, noting there was no difference between IC and PC barrows.

Carcass cutability: Proportional distribution throughout the carcass, not constrained to specific cuts, is important. “IC barrows have a relatively consistent increase in carcass cutability of 2.0 to 2.5%,” he notes.

Fat quality: “We know that the IC barrows are slightly leaner, grow faster and have slightly thinner bellies, so we need to be able to manage fat quality differences. This can be done by adjusting the timing between the second dose and harvest. If a consumer wants a leaner product, you would harvest IC barrows 3-4 weeks post second injection. If they want a little more fat, harvest animals 7-9 weeks post second injection,” he suggests, noting that intramuscular fat can be managed with diet.

Further processing: “About 75% of pork in the United States is further processed,” Boler reminds. Research showed virtually no difference in loin depth in IC barrows vs. PC barrows. IC barrows consistently had a slight reduction in 10th rib backfat and a slight improvement in carcass lean — the packer advantage. But the slightly thinner bellies of IC barrows must be monitored and managed, he explains.

Feeding Management

University of Guelph swine nutritionist Kees de Lange describes the immunologically castrated (IC) barrow as a “fascinating animal.” “Understanding it in terms of feeding management has proven to be a challenge, but it’s exciting too, because it is a new tool to manipulate feed efficiency and carcass quality in pork production,” he says.

“In a discussion about the biology of growth, swine nutritionists like to talk about whole-body protein deposition and how it changes over time. These changes determine optimum market weight, marginal feed efficiency, nutrient requirements and cost of production. Clearly, entire males are superior in protein deposition. They peak later in life, so raising entire males is an advantage,” he explains.

During the grow-finish phase, feed efficiency in entire males can be as much as 15% higher than that in physically castrated (PC) barrows. Based on the various studies, growth performance of IC barrows is identical to entire males up to the second dose of Improvest. After the second dose, the IC males gradually change, which results in higher feed intake, growth rate and whole-body protein deposition.

Based on six growth performance studies conducted in the United States, Improvest reduced feed required per pound of gain by about 7% and improved growth rate by about 3%, when IC barrows were compared to PC barrows over the entire growth period.

Feed intake of PC barrows is about 13% greater than IC barrows before the second dose is administered. After the second dose, the difference is reversed. IC barrow feed intake is about 5% higher, on average, but the difference was 1% in some studies and 9% in others, de Lange explains.

“Predictability of performance after the second dose seems to be poorer than it is prior to that dose. This will have some implications on how we feed those animals in specific units,” he adds.

Feed intake is the key. “Essentially, after the second dose, the physiology of the IC male becomes more like that of a PC barrow. Suddenly, it wants to become fatter and that means it’s going to eat a lot more feed.

In the metabolism studies with individually housed pigs, we saw feed intakes increase by 20-30% within days after the second dose. It’s quite remarkable,” de Lange says. “However, this increase in feed intake appears smaller and more gradual under commercial conditions. The biggest questions that remain are how does group size, pig space, feeder space and maybe genotype affect feed/energy intake after the second dose?”

The PC barrows grow a little faster than the entire males up to when the second dose is given, but the difference is minor, he says. “After the second dose, the IC barrows begin to overtake the PC barrows and their growth rate is 10-15% higher,” de Lange says.

Protein and lysine requirements for the intact males (prior to the second dose) are much higher than are normally fed to grow-finish pigs in North America, he explains. But after the second dose, when feed intake increases substantially, the protein and lysine levels in the diet can be reduced for IC barrows.

“The real opportunity lies in adjusting the feeding program of those animals. Split-sex feeding and phase feeding will become more important, which will have implications for flow and management of those animals,” he adds.

“The carcass yield will always be lower in the IC barrow than the PC barrow because we remove a little extra weight at the slaughter house (testicles, gut fill, etc.). That just means we have to get about 1.2% extra weight on those IC barrows before they are sent to market in order to achieve carcass weights that are similar to PC barrows,” he observes.

About three years ago, Pfizer assembled an international nutrition panel to review nutrient requirements and feeding recommendations for IC barrows. More recently, a North American panel was assembled to review U.S. and Canadian pig performance studies and to update recommendations from the international panel.

The North American panel agreed that nutrient requirements for intact males and IC barrows can be derived using the nutrient requirement model from the new National Research Council (NRC) publication, “Nutrient Requirements of Swine,” 11th edition (available via www.nap.edu or call (800)-624-6242.

Based on observed performance in the six North American studies, the nutrition panel suggests the dietary lysine requirements of IC barrows are similar to lean gilts. Therefore dietary lysine levels that are 104, 108, 112 and 98% of those for gilts are recommended when IC barrow body weights are 55 to 110, 110 to 165, 165 to 220 and 220 to 275 lb., respectively.

“Other nutrients in the diet basically increase in proportion to lysine because most of the requirements are driven by muscle growth and protein deposition,” de Lange explains.

Ractopamine (Paylean from Elanco Animal Health) also changes the physiology of the pig. When fed to Improvest -managed pigs, the responses are additive, which means the nutrient requirements are additive too, he says.

“We don’t need to spend a lot of time estimating the nutrient requirements because we know and understand the animal’s biology sufficiently to say those responses are additive. This is also very exciting because we now have an additional tool to optimize and manage feed efficiency and carcass quality,” he adds.

Payback Potential

In an effort to establish the baseline variables, assumptions and criteria needed to begin to analyze the payback potential of Improvest at the farm level, Kelly Zering, North Carolina State University Extension economist, developed a standard partial-budget analysis. Key assumptions include the need for split-sex feeding, elimination of the materials and labor for castration and a lower pre-weaning mortality and morbidity of intact males. The cost of Improvest and the labor and equipment required to administer two doses was set at $5/pig in the model.

In the extensive partial budget model, factoring in pig performance and carcass differences, the predicted net revenues after costs were $6.36/IC
barrow, including $1.16/male pig weaned, by reducing preweaning death loss. The predicted results are specific to the prices and production parameters used in the model. Vast differences in farm facilities and pig management capabilities will impact return on investment, Zering emphasizes.  

Editor’s Note: Future issues of National Hog Farmer will feature results of research trials studying the impact of Improvest .