Plants contain many different substances. For instance, flavonoids, carotenoids and antioxidants are some of the substances commonly found in plants. These substances are also known as phytochemicals. Some substances in plants can have a negative effect on the body in excess. These substances are also called phytotoxins. One of the most common phytotoxins are goitrogens.
Goitrogens can have a negative effect on the animal because it can block the passage of iodine to the thyroid gland. Ultimately, this can lead to the development of various conditions such as a goiter, shedding problems, growth retardation or lethargy. There are three different types of goitrogens: goitrin, thiocyanates, and flavonoids. When plant stocks are destroyed by, for example, chewing or cutting, the substances goitrin and thiocyanates are formed. Flavonoids, on the other hand, are already naturally present in plant stocks. Some of these substances are good antioxidants, but there are also flavonoids that can be converted to goitrogenic compounds by intestinal bacteria.
In small amounts, goitrogens are not harmful to the animal. However, care must be taken not to feed too many plant stocks high in goitrogens. There are a number of plant stocks that are high in goitrogens such as: spinach, cassava, peanuts, soybeans, kale, broccoli, Brussels sprouts, cabbage, canola, cauliflower, radishes, and rapeseed. It is advised to feed herbivorous animals a variety of vegetables to avoid excess goitrogens. In addition, supplementing iodine is not recommended because animals are sensitive to an excess of iodine.