EVIDENCE FOR THE PRESENCE OF ENDOGENOUS 19-NORTESTOSTERONE IN THE COW PERIPARTUM AND IN THE NEONATAL CALF

Urine samples were collected from five Brown Swiss cows during the 18 days prior to and 11 days after parturition and were analysed for 19-nortestosterone using an enzyme immunoassay. Nortestosterone concentrations ranged from 70 to 130 nmol/l in all samples taken before parturition. The levels declined within two days, and 11 days post partum no nortestosterone was detectable. In urine from newborn calves, maximal nortestosterone concentrations were determined during the first day of life (10.9-120 nmol/l), declining below 7.3 nmol/l until day 3 in most animals and remaining below the detection limit (< 3.6 nmol/l) after day 8 in all animals. There was no obvious difference between cows carrying a male or a female calf nor between newborn male or female calves. Using the combined methods high performance liquid chromatography/enzyme immunoassay and high performance liquid chromatography/gas chromatography-mass spectrometry, the immunoreactivity in urine was identified to be 19-nortestosterone-17-alpha. Although there is unequivocal evidence for the endogenous production of nortestosterone in pregnant cows, its function for placenta physiology, pregnancy anabolism and parturition remains unclear. However, new threshold levels for residue control of nortestosterone need to be fixed in accordance with the endocrine status of the animals.