Reduced anti-Müllerian hormone (AMH) in mares with hemorrhagic anovulatory follicles

Anti-Müllerian hormone (AMH) has been observed to decrease with the development of hemorrhagic anovulatory follicles (HAFs) in mares. Two studies were conducted to evaluate AMH concentration in mares with HAFs compared to seasonally anoestrous and cyclic mares, and to elucidate changes of AMH with the development of luteinised unruptured follicles (LUFs). In study 1, AMH and progesterone were evaluated in seasonally anoestrous, anovulatory (with HAF) and cyclic mares (at mid luteal phase). In study 2, mares in control and LUF groups were treated with 1500 IU/case hCG when they had a ≥32-mm follicle and an endometrial oedema score of three (day 0). Mares in the control group received no further treatment. Mares in the LUF group received 1.7 mg/kg flunixin meglumine at the time of hCG administration, and 12, 24 and 36 h after it. Ultrasonography and blood collection for AMH and progesterone measurement were performed on days 0, 1, 2, 4, 6 and 8. In study 1, AMH concentration was lower in seasonally anoestrous and HAF mares than cyclic mares (P<0.05). Progesterone concentration did not differ between HAF and cyclic mares (P>0.05). In study 2, AMH was not different between LUF and control mares (P>0.05); however, progesterone had a lower concentration and a delayed rise after hCG administration in LUF mares compared with the control group (P<0.05). The results indicated that similar to seasonally anoestrous mares, AMH concentrations decreased in mares with HAFs. LUFs were also found to be functionally different from HAFs.