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(Photo: Tawin Mukdharakosa/Shutterstock)

Pig Sex Is Becoming a Thing of the Past

• July 04, 2014 • 10:00 AM

(Photo: Tawin Mukdharakosa/Shutterstock)

Artificial insemination is much more efficient.

Timon the boar (named after the character in the Lion King) runs around a pen full of young sows. The sows, known as gilts because they have yet to bear piglets, start squealing and frantically pacing the pen. Timon’s job is to identify gilts who are coming into heat and ready to breed. While most of the gilts run away from him, some freeze up, a sign that they’re ready for his advances. As a sow adopts the appropriate stance, Timon realizes this could be his big moment—but alas, Joey Galligan, the intern at Thomas Parsons’ research lab at the University of Pennsylvania School of Veterinary Medicine, swoops in with an almost two-foot-long catheter and artificially inseminates the gilt. Timon is led back out of the room.

Three decades ago, Timon would have had much better luck. Only two to four percent of pig farmers used artificial insemination in the 1980s, says Tim Safranski, the state swine breeding specialist at the University of Missouri in Columbia. Today that figure is closer to 90 percent.

In the 1990s, Safranski and other swine experts began arguing that the time was ripe for shifting the industry over to artificial insemination. Sex was just too inefficient. Letting pigs do things the old-fashioned way meant that a single boar’s ejaculation impregnated just one sow at a time. With artificial insemination, the same sperm could impregnate dozens of sows. With the need for boars thus reduced, farmers would be able to use semen from only the most genetically superior boars. The resulting piglets would be much more similar. Uniformity is important in the meat industry, explains Parsons, because “if we sit down to dinner at a restaurant, both order a pork chop and yours is twice as big as mine, I might go away unhappy.”

Uniformity is important in the meat industry, explains Parsons, because “if we sit down to dinner at a restaurant, both order a pork chop and yours is twice as big as mine, I might go away unhappy.”

Dairy farmers widely adopted artificial insemination for cows several decades before pig farmers did, largely because the process was much harder in pigs. For one thing, cow semen could be frozen without any loss in quality. That meant it could be shipped long distances without spoiling or held in reserve for long stretches of time. Freezing pig semen, however, resulted in 20 percent fewer sows getting pregnant than traditional mating, and those who did get pregnant bore fewer piglets.

Moreover, a pig in heat is quite a different animal from a cow in heat. Cows ovulate, or release an egg, after they’ve come out of heat. So farmers know that artificially inseminating a cow during her heat cycle makes it very likely that she’ll get pregnant. But pigs come into heat and ovulate at the same time. That means pigs have to be inseminated across several days to get the timing right.

In the last few decades, several convergent factors have made artificial insemination in pigs much more feasible. And more desirable too: Whereas a small pig farmer once owned both boars and sows, as farms grew larger, operations grew more specialized. Today, sows, boars, piglets, and even piglets destined to become breeders live in separate facilities. Rather than continually transporting hundreds of boars from farm to farm, it became much more appealing, not to mention cheaper and safer, to just transport semen. Drivers, often retired farmhands, were hired to carry fresh semen from farm to farm, says Safranski. In more remote areas or research farms where shipments tend to be more sporadic, the advent of overnight delivery through companies like FedEx and UPS in the 1980s and 1990s further facilitated the process.

Back in the day, says Mark Estienne, a swine physiologist at a Virginia Tech experiment station in Suffolk, Virginia, a 300-sow farm using natural mating would typically have needed about 20 boars. Now, the same farmer needs just one. Nor is that boar even necessary for actual mating. Like Timon, his job might entail identifying gilts in heat or facilitating the artificial insemination of sows who have recently weaned their piglets and are ready to get pregnant again. Pheromones released in the boar’s saliva help the sows to lock up as they would to prepare for sex, as well as stimulating their reproductive tracts to contract and draw the semen inward.

Today’s farmers are trying to make the process in pigs even more efficient. In the Netherlands, for instance, farmers have produced the same number of piglets using a third less sperm cells than farmers in the United States by inserting the semen deeper inside the sow, which increases its chances of fertilizing her eggs. And Estienne is researching how to bolster the fertility of boars. He’s found, for instance, that supplementing a boar’s diet with omega 3 fatty acids increases sperm counts, although he’s not entirely sure why that is. All these measures make it less and less likely that farmers would resort to mating genetically “mediocre” boars.

Despite his sexual frustration, then, Timon is a lucky fellow. Unlike his many, many brothers who get castrated at birth and live to just six months, he’s managed to retain his genitalia and enjoy his youth. Best of all, every now and then Parsons and his team let him enjoy some quality time with the girls. “We try to let him have one every once in a while,” Galligan says.


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This post originally appeared on Mosaic as “Getting Piggy With It” and is republished here under a Creative Commons license.

Sujata Gupta
Whether discussing the cannibalistic ways of mantis shrimp or shaking the sticky foot of a male African clawed frog, Sujata reports on the strange world of science. She is particularly fond of writing about anything that involves science and food. Her work has appeared online and in print in the New Yorker, New Scientist, Nature, High Country News, Scientific American, Wired, Psychology Today, and other publications.

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