Death rates for female pigs in the US are rising fast, sending alarm bells ringing throughout the farming industry.

The mortality rate rose from 5.8% to 10.2% on farms owning more than 125 sows between 2013-2016, according to one organisation that collects data across 800 companies.

The numbers have been linked to a troubling rise in prolapse – the collapse of the animal’s rectum, vagina, or uterus. In some cases the prolapse itself is fatal. In others the pig is euthanised as a result. Some farms have seen no rise, or much smaller rises, but a separate report last year found that some farms were seeing prolapse causing as many as 25%-50% of sow deaths.

The American Association of Swine Veterinarians has created a sow prolapse working group, but their findings so far have been inconclusive. In April, the National Pork Board announced a multi-year research collaboration with Iowa State University’s Iowa Pork Industry Center designed to get a broad overview of the problem. Iowa is the nation’s top pork producer. The study, which is still under way, aims to collect detailed data from 400,000 sows – or about 13% of the nation’s 3 million working sows – on more than 100 farms across 16 states.

A number of possible causes have been suggested, including vitamin deficiency, mycotoxins in the feed, high density diets or abdominal issues. Some experts blame confinement systems in intensive farming – sows will spend a large percentage of their lives in gestation and farrowing crates that don’t allow them to move around. Modern breeding practices have also been suggested as a causal factor.

Industry figures largely declined to comment but some acknowledged that they are grappling with the issue. “It’s a topic in our meetings, both in the hallways and the meeting spaces,” said Dr Tom Burkgren, executive director of American Association of Swine Veterinarians, a group that educates vets around the country.

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Facebook Twitter Pinterest After piglets are born, the sows are kept in farrowing crates where the young can feed. Photograph: Jo-Anne McArthur/We Animals

An estimated 97% of the US’s 73 million hogs are raised in closed barns or confined feeding operations. In these systems sows often live the majority of their lives in gestation or farrowing crates that don’t allow them to get up or turn around. In this system the average sow produces 23.5 piglets per year – or ten per litter at a rate of 2.35 litters annually. After two to four litters, most sows tend to be replaced by younger gilts who can produce piglets at a higher rate.

Mary Temple Grandin – professor of animal science at Colorado State University and consultant on the design of livestock-handling facilities – told the Guardian that highly focused breeding across the industry has led to unintended consequences. She said that one side effect of selecting for animals that are more fecund is an increased tendency toward lameness.

In the late 1980s, Grandin added, pigs were bred with three traits in mind: rapid weight gain, thin back fat, and a big loin. Now, she added, “They’re breeding the sows to produce a lot of babies. Well, there’s a point where you’ve gone too far.”

“We’ve bred a contradiction into these animals,” says Leah Garces, outgoing executive director of the US branch of Compassion in World Farming. “Over the last few decades, sows to have been bred to have less back-fat – because people don’t want to eat as much fat – but we also want them to produce more and more babies. And that’s not biologically possible; their bones are weak and they don’t have enough fat to support the reproductive process. We’ve bred them to their limit and the animals are telling us that.”

Facebook Twitter Pinterest Pigs at a Niman Ranch farm in the US, a network that focuses on sustainable agriculture. Photograph: Courtesy Niman Ranch

Alternatives

The high incidence of animal loss in confinement systems is one of the main reasons that Paul Willis, co-founder of Niman Ranch (now a subsidiary of Perdue Farms) spent years building an alternative to modern hog farming. “I have a neighbour that has been raising pigs [in a confinement system] … and they have a dumpster, and I can go by there almost any time of the day or week and it’s full of dead hogs,” said Willis.

When he was raising hogs at a smaller scale, perhaps 200 to 300 at a time, and allowing them to spend time outside, engaging in behaviours that are typical for hogs, such as wallowing and building nests out of straw, Willis said he’d lose just “a few animals a year”. Under this system, pigs only produce about half as many offspring a year as they do in industrial systems.

The key in most livestock production is finding a balance between productivity and the health of the animals, said Grandin. “You have to figure out the optimal number of piglets these sows should have. One thing people have trouble with is asking what is optimal – not maximal, but optimal – when it comes to breeding.”

For those pursuing a maximal approach, there are new products like the Hercules Arm, a $7,000 (£5,330) piece of machinery that went on the market in 2017. It is marketed as “a unique and revolutionary way to effortlessly remove … heavy dead pigs from stalls”.

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