Mycotoxins are toxic secondary metabolites produced by filamentous fungi growing on several agricultural products in various stages of production, from planting to transportation and storage. Diseases caused by mycotoxins are called mycotoxicoses and can affect several animal species, including ruminants. Mycotoxin contamination of dairy cattle diets is also a serious concern for human health, since some mycotoxin metabolites may be excreted in milk, especially the aflatoxin M1. This study presents a review of current knowledge on the main mycotoxicoses affecting dairy cattle, especially those caused by mycotoxins produced by species of Aspergillus, Fusarium and Penicillium. The main toxic effects of aflatoxins, fumonisins and trichothecenes in dairy cows are presented, as well as the occurrence of toxigenic fungi and their respective mycotoxins in feed and silage for dairy cattle. A comprehensive description of prevention and decontamination strategies for mycotoxins in dairy feeds is also presented.