Silage maize is one of the main feed components for dairy cattle in Flanders, Belgium. Like many other food and feed crops, maize can be contaminated with mycotoxins, toxic metabolites produced by several fungal species. These mycotoxins may lead to severe health problems. This PhD thesis aimed at exploring the current mycotoxin load in silage maize in Flanders, at harvest as well as during feed-out, and then investigate which crop husbandry, weather, harvest and silage parameters influenced these levels. Over the course of three years, maize was sampled during harvest and after ensiling at more than 100 dairy farms in Flanders. Furthermore, certain specific factors (biofumigation, crop rotation, varietal differences, harvest date,…) were investigated in field trials, in vitro experiments, and a trial using micro silages. With these results, prediction models were developed for the concentrations of six mycotoxin groups in maize at harvest. This research has shown that nearly every maize field and silage is contaminated with multiple mycotoxins, often in high concentrations. Timing of harvest, choice of variety and certain weather conditions influence the mycotoxin levels at harvest, while improper ensiling and a delayed feed-out increase the risk of high mycotoxin levels. Two silage additives were found to reduce deoxynivalenol or even completely eradicate fumonisin levels in maize silage. These results can be used by farmers to help prevent mycotoxin contamination of dairy feed, and hence limit the toxic effects of mycotoxins on their cattle’s health.