Measurement of Anti-Müllerian hormone (AMH) in female dogs is becoming increasingly important in clinical practice. It has been shown earlier that concentrations vary throughout the estrous cycle. AMH concentrations are known to be high during proestrus and estrus, then decrease during the luteal phase and anestrus. Aim of this study was to investigate variations during pregnancy and lactation. Therefore, blood samples were analyzed from 40 pregnant and 19 non-pregnant privately owned dogs of various breeds. One sample was collected from each dog during estrus, three samples during pregnancy, one at three weeks in lactation, and one after weaning. The measured concentrations were compared with those from the non-pregnant dogs, from which samples were collected at the same corresponding time points. AMH concentration in pregnant dogs was highest in estrus (0.63 ng/ml, quartiles 0.40 and 0.87) and remained relatively high during pregnancy. At sampling during lactation the median concentration was significantly lower compared with all other time points (median 0.19 ng/ml, quartiles 0.14 and 0.26). After weaning, AMH increased again to 0.30 ng/ml (quartiles 0.24 and 0.50). During late pregnancy, lactation and after weaning, the AMH concentration was lower in the pregnant dogs compared with the non-pregnant ones. In addition, the significant decline of AMH concentration in pregnant dogs during lactation was not present in the non-pregnant dogs. It can be hypothesized that higher prolactin concentrations may reduce AMH synthesis by inhibiting the secretion of GnRH, FSH, and LH in mammals. In our study we found moderate negative correlation between bodyweight or the number of suckling puppies and AMH concentration. However, since no assay was available, prolactin concentrations were not measured. These findings indicate that pregnancy and lactation status should be considered when interpreting AMH concentrations in clinical practice.
