A strange catastrophe struck Spain’s pig farmers in the spring of 2010. On 41 farms across the country—each home to between 800 and 3,000 pigs—many sows suddenly ceased bearing young.
On some farms, all the sows stopped reproducing. On others, those that did become pregnant produced smaller litters.
When investigators examined the sows and the semen that had been used to artificially inseminate them—it had been collected from different boar studs and refrigerated—they couldn’t find anything wrong. The sperm cells weren’t misshapen. None of the sows were diseased. No microbes or fungal toxins were detected in their feed or water.
Only one factor was common to all the farms and studs: The plastic bags used for semen storage all came from the same place.