Immunocastrated pigs eat less, convert more efficiently, so what’s holding them back in the US?

Imagine a corn field twice the size of Chicago... That’s what the pork industry could potentially save annually if it adopted an alternative to conventional castration.
calendar icon 30 May 2018
clock icon 7 minute read

With about 55 million male pigs marketed each year in the US, if each male pig consumed approximately 80 pounds less in feed, the industry could save about 400 square miles of land used for corn, according to a swine veterinarian with years of experience with the technology.[1]

Indiana-based consultant Larry Rueff, DVM, who oversees the health programs of farms with an annual production of approximately 2 million pigs, is one of a few producers who’s publicly using the technology, which involves a compound known as GNRF (gonadotropin releasing factor analog-diphtheria toxoid conjugate).

Licensed for use in growing pigs by the Food and Drug Administration, GNRF uses the pig’s immune system to reduce the production of androstenone and skatole, which are responsible for boar taint, the odor that emanates from heating pork from an intact boar marketed at weights exceeding 180 to 200 pounds.

Because the average market weight for hogs is 282 pounds [2], the risk of boar taint leaves US pork producers with two options:

  1. Continue to physically castrate males — a procedure that diminishes the faster growth and lean-muscle deposition rate inherent with intact males or barrows while leaving young, castrated pigs more susceptible to potential infection from the procedure [3];
  2. Immunocastration — which involves administering the compound to boars that are at least 9 weeks of age, followed by a second dose 4 weeks later and then slaughter within 3-10 weeks after the second dose. The procedure “lets boars be boars,” Rueff explains, while nearly eliminating the risk of boar taint.

The stakes are high. With an estimated world population of 9 billion expected by 2050, the pork industry can address the need for affordable protein head on. As it seeks to close the gap in feed-conversion rates (currently the industry runs at a 2.69:1 rate [4]), other technologies such as genetic improvements may bring that down to 2:1 by 2025. That translates to 5 million additional pigs on the same amount of feed as today — and it means more affordable pork for everyone.

But the promise of that kind of sustainable future already is here with immunocastration.

So, where’s the catch? According to some producers, several of the nation’s biggest retailers have pushed back on the packers, for fear that this technology is difficult to explain to consumers. As a result, most packers decline to accept the immunocastrated pigs.

But make no mistake: The technology, which has been approved in the US since 2011 and widely used by pork producers in more than 60 countries, is quietly gaining traction in the US market as the pork industry looks for ways to further improve efficiency and reduce its carbon footprint.

Major benefit in feed conversion

The production efficiencies gained by allowing male pigs to remain intact means they eat less feed and create less waste. This has the potential for an incremental reduction in the carbon footprint by as much as 3.6% (measured in CO2 equivalent per kilogram of pig live weight) versus barrows [5] (Table 1).

Table 1. Average wean-to-finish productivity in conventional production

Source: The Pork Checkoff [6]

Back in Indiana at Rueff’s farm, he has witnessed improved feed conversion firsthand for years.

Housing 25 pigs per pen in 10 pens, he moves them to finishing at 10 weeks of age and to market 3 months later. The first group of immunocastrates showed a 10% improvement in feed efficiency.

“That goes right into producers’ pockets,” Rueff says, referring to the feed savings. “It is sustainable; we’ve sustained it so far. We’ve always known boars convert feed faster than barrows. Immunocastration allows boars to express their natural physiological benefits.”

With some recent adjustments to the diets (such as increased lysine and phosphorous), the feed conversion has improved even more.

Rueff has collected data on the performance of the immunocastrated pigs over 12 groups since January 2014, and the numbers are promising: The last group of 250 that he ran through from wean to market had a feed conversion of 2.21 and an average daily gain of 2.12 pounds per day. They were marketed at 300 pounds.

“We have achieved two-tenths (0.2) of a pound improvement in feed conversion over good performing, conventionally castrated barrows,” he says.

ROI on costs

Although feed remains upward of 60% of the cost of raising a pig to market weight, corn is cheap now. Still, the market is never stable, says David Pyburn, DVM, senior vice president of science and technology at the National Pork Board. At the end of November, it was $3.49 per bushel; the yearly average for 2014/15 was $3.70, and the average for 2015/16 was $3.61 — but that’s only half as much as corn cost/bu in the 2012/13 marketing year. [7]

Using immunocastration, product and administration costs total about $5 per head. So, producers do have legitimate concerns about the costs of immunocastration when feed prices are so low. “Right now, feed costs are fairly low, so that’s probably not a huge driver [to switch from conventional castration]. But that fluctuates. We’ve had some great harvests [of corn] over the last few summers, and lately global harvests have been good,” Pyburn adds.

Other factors to consider are actual feed consumption. For example, pigs stay in the nursery barn for about 6 to 8 weeks consuming a corn and soybean meal diet and eating as much as 4 pounds a day. During their 16 weeks in the finishing barn, they consume more than 6 pounds of feed daily [8] .

Consumer preferences are changing

“We’ve now got an animal that’s better at laying down muscle,” Pyburn adds, referring to most commercially raised pigs. “We honed our production to allow for more muscle and less fat — maybe to the point of the extreme where we need to look at putting more marbling back into the muscle cuts.”

If the pork industry heads in that direction, that could heighten interest in immunocastration. Research shows that after the second dose of the FDA-approved compound, intact immunocastrated boars begin to eat substantially more feed per pound of gain and begin to increase the amount of fat in the carcass, attaining a desirable fat level for primal cut characteristics.[9] And when market conditions force average sell-weights down, producers simply need to time the second dose to ensure that the appropriate amount of fat accumulates on lighter carcasses to meet consumer preferences and avoid erosion of carcass values.

It looks like times are changing.

Pork belly prices continue their annual spring acceleration at retailers looking to take advantage of holiday features, and foodservice operators also have become “consistent large users of bellies” on burgers, sandwiches and salads, according to a June 2017 edition of the Daily Livestock Report, published by Steiner Consulting Group.[10]

“Consumers have to love our product. People want to have an enjoyable, memorable eating experience that they want to repeat. That’s all about tenderness and taste,” Pyburn adds. “It’s going to take a little bit of time [to adjust to consumers’ changing preferences]. It’s a couple-year process, but lucky for us, our generations turn over pretty quickly.”


1. Rueff L. Personal communication, December 5, 2017.
2. Pork Checkoff. Typical market pig today. National Pork Board and EMI Analytics. Updated 8.15.2017. Available at Accessed Dec. 21, 2017.
3. Dunshea F. Castration in the swine industry and the impact on growth performance — physical versus vaccination. London Swine Conference – Focus on the Future. 2010:85-97.
4. Pork Checkoff. Industry Benchmarks. Accessed April 4, 2018.
5. Environdec. Environmental Product Declaration for Improvac. Available at Accessed Nov. 30, 2017.
6. Pork Checkoff. Average Wean-to-Finish Productivity. Available at Accessed Nov. 30, 2017).
7. US Calendar Year Average Corn Price. Calculator available at Accessed Nov. 30, 2017).
8. Pork Checkoff. Life cycle of a market pig. National Pork Board. 2016. Available at Accessed Nov. 30, 2017.
9. Costa E Silva LC, Barbsa RD, Silveira ETF. Effects of ractopamine hydrochloride and immunological castration in pigs. Part 2: belly quality characteristics and fatty acid composition. Food Sci. Technol, Campinas. July-Sept. 2017;37(3):404-410.
10. Daily Livestock Report. June 20, 2017;15(114). Available at . Accessed Nov. 30, 2017.

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