The objective of the research study was to discuss risks to animal health caused by natural harmful substances, i.e. phytotoxins and mycotoxins derived from feed in view of their adverse impact on milk quality and, consequently, on human health. As the most harmful compounds derived from feed are commonly indicated alkaloids, glycosides, saponins, essential oils, and organic acids as well as toxins produced by mould. Less harmful are glucosinolates, coumarin and derivatives of furanocoumarin, lectins, and, also, phytoestrogens. Both the harmful compounds naturally occurring in fresh forage and in other bulky feeds and the mycotoxins are a potential threat to health and life of animals since they affect productivity of animals as well as the quality of raw materials including milk. The biggest threat to animal and human health is aflatoxin B1 because of its proven carcinogenic and mutagenic effects. However, as it is indicated by RASFF reports, such risks rarely occur. It results from two facts: animals selectively take and consume feed, particularly the grazing animals; farmers take actions under the Good Agricultural Practices.