The verdict, which can be appealed, was handed down on Tuesday by federal judge Djalma Gomes.
"Animals are not things. They are sentient living beings, that is, individuals who feel hunger, thirst, pain, cold, anguish, fear," Gomes wrote in the ruling.
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The National Forum for the Protection and Defense of Animals, a Brazilian NGO, had filed a lawsuit in a Sao Paulo court in 2017 requesting all live cattle exports be banned.
The animal rights group called Gomes's ruling "historic" for its recognition of "the suffering caused to animals ... in an activity similar to human trafficking at the time of slavery."
Carlos Favaro, Brazil's agriculture minister, told Reuters on the sidelines of a beef industry event he had not spoken with the solicitor general about whether the federal government would appeal the decision.
He said court orders must be complied with, but defended Brazil's live cattle trade, saying overseas buyers would not invest in livestock that may potentially lose weight during transportation.
He said "the accommodations" the animals travel in are adequate and "favor" the continuation of the cattle's development.
Brazilian food company Minerva (BEEF3.SA), a leading beef supplier live cattle exporter in South America, had no immediate comment on the decision.
Reporting by Ana Mano; editing by John Stonestreet