Excessive copper in feed not merely undermines animal health but affects food safety

Background: Blackened intestines in slaughtered pigs have been commonly observed in China in recent years. However, no cause has been reported. Objectives: We attempted to determine whether the blackening of the pig intestine was related to an excess of copper (Cu) in their feed. Methods: In this study, we observed and collected porcine intestines in small- and large-scale pig slaughterhouses in Shandong province from May to October 2018. Twelve types of metal ions were detected in the black intestinal samples. Results: The Cu level in the intestine samples was mostly higher than the Chinese national limit for food. Further study showed that Cu supplementation in most commercial porcine feed also exceeded the national standard. An animal model (mouse) that could mimic the intestinal blackening in pigs was established. Compared to control mice, Cu accumulated in the liver and intestines of mice fed an excessive Cu level, confirming the excessive Cu in the feed may be considered the major cause of blackened porcine intestines. Microscopic examination revealed that black intestines had many particles containing Cu in the lamina propria of the intestinal mucosa, and the intestinal mucosal epithelial cells showed degeneration and necrosis. Conclusions: In conclusion, overuse of Cu in animal feed can lead to animal poisoning and Cu accumulation in animal products. Such overuse not only harms the health of livestock but can also affect public health.