Anti-Müllerian hormone concentrations in female rabbits and its relation to spay status, pseudopregnancy and ovarian follicle numbers.

Anti-Müllerian hormone (AMH), known for its role during foetal sexual differentiation, is secreted by the Sertoli cells in males and the granulosa cells in females during post-natal life. As serum AMH concentrations correlate with follicle numbers, AMH is utilized as a marker of ovarian reserve in many species. In dogs and cats, AMH is used as a diagnostic tool to determine spay or neuter status. In the available literature, no research regarding serum AMH levels in rabbits has been published yet. The objectives of the present study were to (1) measure serum AMH concentrations in female rabbits and investigate the value of AMH as a diagnostic tool to differentiate between spayed and intact does and (2) relate measured AMH levels to pseudopregnancy and ovarian follicle numbers. For AMH measurement, serum samples were obtained from sexually intact (n = 64) and spayed (n = 22) female rabbits. Spayed does were of various breeds; intact rabbits were Zika hybrid rabbits. In the intact does, AMH measurement was complemented by determination of progesterone levels, gynaecological examination and histopathological evaluation of the uterus and ovaries, including follicle counts. Serum AMH and progesterone concentrations were measured using a human-based chemiluminescence immunoassay (CLIA) and an enzyme-linked fluorescence assay (ELFA), respectively. Depending on progesterone levels, sexually intact does were classified into follicular (n = 52) or luteal phase (n = 12). Median serum AMH levels were 1.53 ng/ml (range 0.77-3.36 ng/ml) in intact and 0.06 ng/ml (range ≤0.01-0.23 ng/ml) in spayed does. AMH concentrations between the intact and spayed rabbits differed significantly and did not overlap (p < .001). Receiver operating characteristic (ROC) curve analysis yielded a sensitivity and specificity of 100% for a cut-off level of 0.50 ng/ml. Follicular or luteal phase had no significant influence on measured AMH levels (t = 0.061, df = 62, p = .951). While the number of secondary follicles correlated significantly with AMH concentrations (r s  = 0.410, p = .001), the number of primary or antral follicles did not (r s  = 0.241, p = .055 and r s  = 0.137, p = .281, respectively). In conclusion, a single determination of serum AMH concentrations was adequate to distinguish spayed from intact female rabbits. Among sexually intact individuals, whether does were in follicular or luteal phase had no significant influence on measured serum AMH concentrations. The relationship between small growing follicles and AMH levels as described in other species could be partially confirmed, as secondary follicles correlated significantly with AMH.