Veterinary treatment of cows with isoxsuprine for a caesarian section may temporarily lead to residues in hair of both cow and calf

Isoxsuprine is a beta-agonist that can be used for growth promotion in cattle, but it is also used as registered veterinary medicine. To investigate if veterinary treatment of cows could lead to residues of isoxsuprine in the hair of their newborn calves, an animal experiment was performed. Four cows, treated on veterinary indication with isoxsuprine lactate (Duphaspasmin) before a caesarian section, were included in the experiment. Hair samples from cows and from their calves were analyzed. The animals were shaved every week for 16 weeks and levels of isoxsuprine were measured in hair. In the cows, the levels of isoxsuprine were highest (>15 µg/kg) just after administration of the isoxsuprine lactate. After two weeks in two cows, a sort of plateau was reached and then the levels decreased. After approximately 10-15 weeks the levels were around the CCa level of the method used (0.5 µg/kg). In calves, for the first two weeks after birth, no isoxsuprine was found above CCa level in three of the four animals. At about 20-30 days old, a maximum concentration of 4 µg/kg was found. Then the levels dropped again under the CCa level, after 60 days no levels above CCa level were found. In one animal, the levels never reached CCa level. We conclude that veterinary treatment of cows with isoxsuprine may temporarily lead to low levels of isoxsuprine in the hair of their newborn calves which can be measured for a maximum of 60 days after birth.