Biological Functions and Clinical Applications of Anti-Müllerian Hormone in Stallions and Mares

Abnormal mare behaviour is rarely associated with changes in hormonal markers of granulosa cell tumours: A retrospective study

BACKGROUND

Abnormal or undesired mare behaviours are often assumed to be associated with ovarian abnormalities.

OBJECTIVES

We aimed to determine the incidence of abnormal behaviours and their association with concentrations of one or more ovarian hormones associated with a granulosa cell tumour (GCT).

STUDY DESIGN

Retrospective descriptive.

METHODS

A total of 2914 hormonal profile samples submitted with the words behave, behaviour, or behaving in the submission history were analysed. The association between reported abnormal behaviours and concentrations of testosterone, anti-Müllerian hormone (AMH), inhibins and inhibin-B were assessed. Statistical analysis was performed using a Chi-squared test of association.

RESULTS

Of the 2914 cases that were submitted due to behaviour issues, 2506 (86%) did not have any of the measured hormones reach GCT-like concentrations. The remaining 408 cases had either one (63%), two (25.5%), or three (11.5%) hormones with concentrations consistent with those from confirmed GCT cases. Testosterone had the lowest percent of GCT-like values among the cases (7.7%), compared with AMH (9.4%), inhibins (9.6%) and inhibin B (8.7%). Stallion-like behaviour was significantly associated with increased concentrations of all four hormones. In contrast, aggression, oestrous and other abnormal behaviours were significantly less likely to be associated with increased concentrations of the hormones.

MAIN LIMITATIONS

Retrospective study, using sample submission history.

CONCLUSION

Overall, the abnormal behaviours among mares, except the stallion-like behaviour, were not associated with increased ovarian hormones. These results highlight the common misassumption about the involvement of the ovaries in 'abnormal behaviours' or 'undesirable behaviours' of mares.

Limited association between stallion-like behavior and hormonal indicators of testicular remnants in geldings

Persistent stallion-like behavior is a common sign of cryptorchidism in supposed geldings. The presence of testicular tissue can be evaluated by analyzing hormones such as testosterone and anti-Müllerian hormone (AMH). Here, we used hormonal analysis to investigate relationships between the likely presence of testicular tissue and stallion-like behavior in samples submitted from presumptive geldings (n = 1,202), retrospectively. Most geldings with stallion-like behaviors had serum concentrations of testosterone (851/1,056; 80.6 %) and AMH (682/877; 77.8 %) below the laboratory reference range for cryptorchids (< 60 pg/mL and ≤ 0.15 ng/mL for testosterone and AMH, respectively). A total of 13 samples (13/716; 1.8 %) showed AMH concentrations typical for geldings but testosterone above the cryptorchid range. Conversely, 31 samples (31/716; 4.3 %) had high AMH, suggesting cryptorchidism, but testosterone concentrations implied no testicular tissue. Among the cryptorchid stallions, the AMH and testosterone concentrations did not vary based on the season. However, age categories affected the concentration of both hormones among the presumptive true cryptorchid stallions. The results of this study demonstrate that undesirable behavior in geldings is rarely associated with the presence of testicular tissue, as assessed by these two hormonal biomarkers. This information highlights the complexity of behavior and demonstrates that persistent stallion-like behavior in geldings could be related to factors other than the presence of testicular tissue.

Assessment of anti-Müllerian hormone in mares' transitional period and in relation to fertility in elderly mares

Anti-Müllerian Hormone (AMH) has been linked to reproductive tract abnormalities in mares and stallions. This study aimed at evaluating AMH as a biomarker for two reproductive conditions in mares. In the first part of this study, plasma AMH was evaluated as an early indicator of the onset of cyclicity in mares in the transitional period from the anovulatory phase during winter anoestrus to the cyclic phase during the breeding season. Ten mares between 8 and 17 years old were included in the experiment which lasted from mid-February until the end of April. Ovarian activity was monitored with ultrasonography three times per week, the detection of a corpus haemorrhagicum/luteum was documented and antral follicle counts (AFC) were recorded. Blood samples were collected weekly by jugular venipuncture during the whole study period to compare AMH concentrations before and after the first ovulation of the year. The second objective was to evaluate if plasma AMH concentrations in middle-aged mares are linked to fertility and could serve as a prognostic marker in that age group. A total of 41 privately-owned clinically sound mares aged between 12 and 21 years of various breeds were inseminated with fresh or frozen semen. Mares were scanned between day 14 and 20 and the "early pregnancy rate" included only positive pregnancy examinations after the first observed cycle in the season of each mare. Potential associations between the early pregnancy rate in the first cycle and the explanatory factors AMH concentrations, age, status of the mare, stud, development of post-breeding endometritis, number of inseminations and semen type were analysed using logistic regression models. In the first part of the study, correlation between AMH and AFC for the whole study period (P = 0.0002, ρ = 0.55) as well as prior to (P = 0.008, ρ = 0.58) and after the first ovulation (P = 0.0007, ρ = 0.69) were observed. However, AMH concentrations before and after the first ovulation of the year were not statistically different. The second part of the study revealed no association between early pregnancy rate and AMH concentrations or any of the other mentioned factors. In conclusion, this study showed no evidence of a difference between AMH concentrations before and after the first ovulation of the year thus not supporting the use of AMH as a biomarker to predict the onset of cyclicity in mares. We could furthermore not show a relationship between plasma AMH concentrations and early pregnancy rates in this cohort of animals.

Anti-Müllerian Hormone and OPU-ICSI Outcome in the Mare

Anti-Müllerian hormone (AMH) reflects the population of growing follicles and has been related to mammalian fertility. In the horse, clinical application of ovum pick-up and intracytoplasmic sperm injection (OPU-ICSI) is increasing, but results depend largely on the individuality of the mare. The aim of this study was to assess AMH as a predictor for the OPU-ICSI outcome in horses. Therefore, 103 mares with a total follicle count above 10 were included in a commercial OPU-ICSI session and serum AMH was determined using ELISA. Overall, the AMH level was significantly correlated with the number of aspirated follicles and the number of recovered oocytes (p < 0.001). Mares with a high AMH level (≥2.5 µg/L) yielded significantly greater numbers of follicles (22.9 ± 1.2), oocytes (13.5 ± 0.8), and blastocysts (2.1 ± 0.4) per OPU-ICSI session compared to mares with medium (1.5-2.5 µg/L) or low AMH levels (<1.5 µg/L), but no significant differences in blastocyst rates were observed. Yet, AMH levels were variable and 58% of the mares with low AMH also produced an embryo. In conclusion, measurement of serum AMH can be used to identify mares with higher chances of producing multiple in vitro embryos, but not as an independent predictor of successful OPU-ICSI in horses.

Case report: The case of a 17 kg ovarian granulosa cell tumor in a Breton draft mare

Granulosa cell tumor (GCT) is a benign tumor which affects the mare's ovaries. In this report, a case of unilateral GCT in an ovary, which weighed 17.04 kg, of a 9-year-old Breton draft mare is described. A transrectal ultrasonography exam revealed a unilateral multi-cystic enlarged ovary. Laparoscopic ovariectomy was difficult due to enlargement of blood vessels in the ovarian broad ligament. The mare was necropsied, and the pathological changes in the GCT-affected ovary and unaffected ovary were evaluated. The ovarian mass in the GCT-affected ovary had a cribriform pattern and was positive for anti-Müllerian hormone (AMH) and its receptor (AMHR2). The contralateral ovary showed no follicular development and was negative for AMH. AMHR2 was positively expressed in stromal cells. The AMH concentration in plasma was 4,210 ng/ml. This is the first report showing the presence of AMH (2,210 ng/ml) in ascites fluid, and it also shows that laparoscopic ovariectomy might not be suitable for larger ovaries affected by a GCT. Ultrasonographic, endocrine, and histopathological analyses were helpful for making a definitive diagnosis of GCT in this mare.

Serum concentrations and testicular expressions of insulin-like peptide 3 and Anti-Müllerian hormone in normal and cryptorchid male horses

Insulin-like peptide 3 (INSL3) is an important hormone for testicular descent during embryonic development and a factor for assessing functional status of Leydig cells of testes, but there is limited number of equine studies. Anti-Müllerian hormone (AMH) is a useful diagnostic marker for cryptorchidism in horses. This study aimed to compare serum concentrations and testicular expression intensity of INSL3 and AMH in intact and cryptorchid male horses. Serum INSL3 concentrations in intact (n = 9; mean ± SEM, 19.9 ± 5.9 ng/mL) and noncastrated unilateral cryptorchid (UC) male horses (n = 16; mean ± SEM, 16.8 ± 4.1 ng/mL) were higher compared with hemicastrated unilateral cryptorchid (HCUC) male horses (n = 9; mean ± SEM, 3.8 ± 0.7 ng/mL) (P < 0.05). And serum INSL3 in bilateral cryptorchid (BC) male horses (n = 4; 1.9 ± 0.4; mean ± SEM, ng/mL) were lower compared with intact male horses (P < 0.05). Serum AMH concentrations in BC male horses (n = 3; mean ± SEM, 30.6 ± 4.8 ng/mL) were higher compared with intact male horses (n = 5; mean ± SEM, 12.2 ± 3.9 ng/mL) (P < 0.05). Immunostaining of scrotal and cryptorchid testis showed that Sertoli cells were positive for AMH, and Leydig cells were positive for INSL3. Staining intensity of AMH was higher in cryptorchid testis than in scrotal testis (P < 0.05). Furthermore, AMH expression intensity was higher in abdominal testis than in inguinal testis (P < 0.05). Immunostaining intensity of INSL3 in the testis was positively correlated with serum INSL3 (r, 0.7; P < 0.01), seminiferous tubule area (r, 0.727; P < 0.01), and Johnsen score for spermatogenesis (r, 0.604; P < 0.05), whereas immunostaining intensity of AMH in the testis was negatively correlated with seminiferous tubule area (r, -0.814; P < 0.01) and Johnsen score for spermatogenesis (r, -0.807; P < 0.01). Our findings suggested that AMH is a good biomarker for diagnosing cryptorchidism in male horses, in addition to INSL3 values to assess the testis of intact and cryptorchid male horses.

Inhibin-A and inhibin-B in cyclic and pregnant mares, and mares with granulosa-theca cell tumors: Physiological and diagnostic implications

Studies in mares have examined serum inhibin concentrations using immuno-assays unable to distinguish dimeric inhibin-A from inhibin-B isoforms. Inhibin-A and inhibin-B immuno-assays were used to investigate concentrations in cyclic mares, young and old (6 vs 19 years old, respectively) mares following hemi-ovariectomy, mares during pregnancy and in mares with confirmed granulosa cell tumors (GCTs). Mares with inter-ovulatory intervals of 26 days had ovulatory peaks of inhibin-A averaging 80 pg/mL with a mid-cycle nadir of 5 pg/mL. Inhibin-A and inhibin-B concentrations were highly correlated (r = + 0.79, P < 0.01) though peak and nadir concentrations of inhibin-B were not significantly different. However, the ratio of inhibin-A to inhibin-B (A/B) changed significantly through the cycle, highest at ovulation and <1 (more inhibin-B than -A) at mid-cycle. Two mares with grossly extended inter-ovulatory intervals demonstrated mid-cycle inhibin-A (and inhibin-B) excursions suggestive of follicular waves. Follicle-stimulating hormone was negatively correlated with inhibin-A and -B concentrations in all 6 mares. Hemi-ovariectomy in young mares resulted in a significant decrease in inhibin-A and inhibin-B concentrations one day later (P < 0.05) but older mares did not, suggesting a possible extra-ovarian source(s) of these hormones. Both inhibin isoforms dropped to very low levels during pregnancy (P < 0.0001), inhibin-A (P < 0.0001) more rapidly than -B (P < 0.05), so that inhibin-B became the predominant measured form throughout most of gestation (P < 0.05). Mares with confirmed GCTs had elevated inhibin-B concentrations more reliably than inhibin-A but neither inhibin-A or -B was correlated with anti-Müllerian hormone concentrations. Collectively, concentrations of inhibin-A and -B were aligned with physiological events in healthy mares, though more pronounced cyclic changes were seen with inhibin-A. Inhibin-B concentrations were significantly associated with GCTs (P < 0.01), inhibin-A concentrations were not. While both inhibin-A and -B concentrations track physiological events such as cyclic follicular activity, only inhibin-B concentrations effectively signal ovarian neoplasia in mares.