By 381 days, they could neutralise 96% of strains tested in the lab.
Dr Dennis Burton, a fellow researcher, said: "The potent responses in this study are remarkable.
"Unlike human antibodies, cattle antibodies are more likely to bear unique features and gain an edge over HIV."
Unusually for human antibodies, the broadly neutralising ones have a long and loopy structure. Cow antibodies are inherently more long and loopy.
So the cow immune system finds making the antibodies easily.
It is thought the cow's "ruminant" digestive system which ferments grass in order to digest it is a Wild West of hostile bacteria. So the animals have developed the antibodies needed to keep them in check.
It means cattle could eventually become a source of drugs to make more effective vaginal microbicides to prevent HIV infection.
However, the real goal is to develop a vaccine that encourages the human immune system to make the antibodies it currently finds a struggle.
That remains a significant challenge, but the cattle study could help point the way.
Dr Anthony Fauci, the director of the US National Institute of Allergy and Infectious Diseases, said: "From the early days of the epidemic, we have recognized that HIV is very good at evading immunity, so exceptional immune systems that naturally produce broadly neutralizing antibodies to HIV are of great interest - whether they belong to humans or cattle."