No known toxins so safe in moderation, although as a member of the Brassica family it shouldn't be fed to excess.
Please be aware that two or more goitrogenic plants should not be fed in conjunction with each other, and the sum total of goitrogenic foods should not exceed the guideline for a single plant of 'in moderation' (amber-green) or 'sparingly' (amber-red). This will ensure that goitrogenic consumption stays within safe limits.
Goitrogens compromise thyroid activity by interfering with iodine uptake and this could cause liver and kidney lesions. Thyroid hormones are associated with skin cells, growth and metabolism so any interference with this can lead to problems with shedding and cause slow growth. Goitrogenic glycoside can be found in plants of the Brassica and related families, including Cabbage, Kale, Spinach and some hot peppery-flavoured plants like Wild Mustard, and can also contribute towards the formation of kidney and bladder stones.