Compounds in Milk Accompanying Feeding of Ethoxyquin

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Abstract
A feeding trial was conducted to deter- mine if ethoxyquin, or its residues, is transferred from feed to milk when added to feed at 0.015% of the dry matter intake. A very low concentration (less than 7 t~g/ liter) of ethoxyquin was detected in milk by a fluorimetric procedure and by thin layer chromatography. Feeding ethoxyquin did not increase milk tocopherol, but was accompanied by appearance in milk of a compound (not yet identified) that inter- fered in the determination of ethoxyquin by a fluorimetric method, and in the determina- tion of tocopherol by a method used before in our laboratory. In a previous study (2), the data indicated that feeding ethoxyquin to cows at 0.015% of their dry matter intake resulted in the transfer of ethoxyquin to milk with a marked increase in tocopherol in milk. Deficiencies in the meth- od used for the determination of ethoxyquin in milk were noted. Our objectives for continuing studies were to measure and characterize compounds that ap- peared in milk when cows were fed ethoxyquin, and report results of experiments in which cows received ethoxyquin at 0.015% of their dry mat- ter intakes. Experimental Procedure Ethoxyquin supplementation. The three Hol- stein cows used in this study ate at least 15 kg of dry matter per day. At each milking for 13 days, each cow was fed concentrate containing 1.125 g of ethoxyquin, thus providing a maxi- nmm concentration of 0.015% of the dry matter intake. Samples of the cows' milk were taken three times weekly (at the Monday, Wednesday, and Saturday Pg milkings) for one week before the ethoxyquin supplementation, during supple- mentation, and for five days after supplementa- tion. Ethoxyquin or ethoxyquin equivalents. Eth- oxyquin or an unidentified compound(s) that appeared in the milk when ethoxyquin was included in the ration were determined by three methods. The results are expressed as equiva- lent concentrations of ethoxyquin.