To clarify the clinical findings in mares with granulosa theca cell tumor (GTCT) and to determine reproductive activity after surgery, 16 mares with GTCT were studied. The GTCTs were found in 10.4 ± 0.9 year olds. The clinical signs manifested by the affected animals varied, and the mares showed abnormal behavior, that is, anestrus (n=5), continuous estrus (n=8) and stallion-like behavior (n=3), but most of the affected mares (11/16) were sterile for long periods (1-4 years), and in four animals GTCTs were detected at the post-partum period. In 11 of the 16 animals, the ovary containing tumor was enlarged on the right side, whereas the contralateral ovary was atrophied in all the 16 animals. Mares in which the affected ovary was surgically removed in the non-breeding season (n=8) had estrus 2.6 months earlier and became pregnant 2.9 months earlier than those operated on (n=8) in the breeding season, by resuming the reproductive function in the remaining ovary. All three mares that died from hemorrhage after the surgery were operated on in the breeding season. From these results we confirmed that GTCT is related to sterility for long periods in mares and that surgical removal of the affected ovary is effective in restoring reproductive function. And it is also suggested that the affected ovary should be removed in the non-breeding season.

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Control of ovulation in mares obviously has many advantages in a breeding program. Two pony mares were challenged against synthetic Gonadotropin Releasing Hormone (GnRH) agonist (Deslorelin) for six consecutive cycles. Clinical and endocrinological findings after treatment (n=6) with GnRH agonist were compared with those of the control findings before treatment (n=3) of the same mares. The time interval from administration of the GnRH agonist till ovulation (43.5 ± 4.0 hr) and the length of the estrous cycle (19.5 ± 1.0 days) at the time of treatment were significantly (p<0.05) shortened as compared with those of the control. A preovulatory sharp rise in plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH) was also noticed 24 hr from the time of GnRH agonist injection and one day prior to ovulation in the studied mares, but there were no significant differences before and after treatment with GnRH agonist on the levels of ir-inhibin, progesterone (P) and estradiol-17 β (E₂). It seems likely that GnRH agonist is beneficent in reducing the number of matings needed for conception in a natural mating program and that ovulation in mares may be induced by a sharp preovulatory rise in LH and FSH.

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In splenectomized Thoroughbred horses (Group S), the plasma haptoglobin (Hp) concentration was increased by the operation but thereafter significantly decreased to a lower level than before the surgery. The red cell haemolysis rate in a hypotonic salt solution and haemoglobin (Hb) binding Hp after exercise in Group S were significantly lower than in control horses (Group C). These results suggest that: 1) the spleen accelerates the fragility of the red cell membrane; 2) osmotic sensitive red cells are easy to haemolyze during exercise; and 3) the haemolysis during exercise increases the Hb-binding Hp level in plasma and then accelerates the synthesis of Hp in liver. Therefore, plasma Hp is a clinical indicator of red cell membrane fragility and haemolysis in a blood vessel during exercise.

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We report four cases resembling Australian stringhalt observed for the first time in Japan. Between June and July 2000, three of four 4-year-old thoroughbred mares that had been grazed on the same pasture suddenly suffered exaggerated flexion of both hindlimbs. Subsequently, the remaining horse also exhibited mild stringhalt in October. The last horse recovered without treatment one month after occurrence, but the other three horses exhibited severe stringhalt even 5-6 months after occurrence. In one horse, endoscopic examination revealed a left laryngeal hemiplegia. Three of four cases were treated with a combination of drug based treatment (baclofen and phenytoin) and exercise. While phenytoin was effective in treating the stringhalt, the baclofen had no effect. Once the stringhalt improved, treadmill exercise was started to improve hindlimb function. As a result, two of the three horses were able to canter. Three cases underwent electromyography examination and motion analysis. Before treatment, high amplitude electric discharges were observed in the long digital extensor muscle and the lateral digital extensor muscle in the swing and stance phase. The angle of each joint flexed extensively in the swing phase. While Australian stringhalt may heal spontaneously over time, therapy with phenytoin and exercise may hasten a cure.

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