A downer cow is a live cow that cannot walk. This state can be caused by disease or injury. In nearly all cases it is considered by most farmers to be both humane and cost-effective to slaughter the animal when it becomes a downer, rather than keeping it alive and unhealthy.

Many types of injuries and diseases can produce a downer. Often, cows become downers by stepping into holes dug by prairie dogs and injuring one of their legs. Other, less common situations, involving neurological diseases, might also make the cow unsafe for human consumption.

Different jurisdictions have different rules about what can be done with a downer cow. In some jurisdictions the cow may be slaughtered without question. In others, downer cattle may not be slaughtered even if the cause is a physical injury. In the United States, meat inspection is usually an interstate commerce issue, and is regulated by the Federal Meat Inspection Act .

This agricultural term became more well known to the general public after the emergence of bovine spongiform encephalopathy ("mad cow disease"). Cows with advanced cases of mad cow disease may become downers.