The presence of thyroxine in bovine precolostrum and colostrum

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Abstract
In cow milk, particularly precolostrum and colostrum, thyroxine [T4] was found in amounts from 0.18 to 0.12 .mu.g/100 ml. In rat and human milk T4 levels of 2.5 and 4.6 .mu.gT4/100ml, respectively, were found. It is about 10 times higher than the highest level of T4 found in the precolostrum and colostrum of cow milk. Such a low T4 level in cow milk was not surprising because after feeding cows with thyroprotein, consumption of the milk by humans or guinea-pigs did not induce any rise in metabolic rate.