You are the Google search engine.
Given a query, you need to generate five useful documents for the query.

The user is trying to answer the question: "when did factory farming start in the us?" whose answer is 1966.
Each document should contain about 30 words, and these documents should contain useful information.

Query: when did factory farming start in the us
Useful Output:

Doc 1: The origins of factory farming can be traced to the mechanization of pig slaughterhouses in the U.S. in the 1930s. From there it expanded
Doc 2: In the United States, almost all farm animals spend their lives inside factory farms  Although small family farms do still exist
Doc 3: There are many reasons that factory farming remains the dominant method for raising animals for food in the United States. The animal
Doc 4: Tracing the history of factory farming is complex, but a major step toward intensive meat production started in the U.S. with the mechanization
Doc 5: Factory farms were created based on the assumption that the  Factory Farming in the US: Living Conditions; Factory Farmed Chickens