Abstract: The functional anatomy of the thoracolumbar (TL) spine is considered in relation to the horse's ability to perform at speed and to jump. The morphological features quite clearly show the relative inflexibility of the equine back and this was confirmed by some experimental studies. Fresh post mortem specimens from 5 Thoroughbreds were used to estimate the limits of dorsoventral movement of the TL spine from mid-thoracic to the cranial lumbar (T10-L2). The individual spinous processes could be moved a mean 1.1-6.0 mm on maximum ventroflexion and 0.8-3.8 mm on dorsiflexion. The overall flexibility of the back was found to be 53.1 mm. Caudal to the mid-point of the back (T13) there was virtually no lateral or rotatory movement of the spine possible. The pathogenesis of some of the common causes of back trouble are discussed including the so-called vertebral subluxation and its treatment by chiropractic manipulation. From an anatomical viewpoint, this condition appears to be a misnomer and may simply be attributable to muscular imbalance leading to aspastic scoliosis.

Abstract: The influence of steroids of adrenal cortical origin on estrous behavior in the ovariectomized mare was evaluated by adrenal suppression via dexamethasone (DEX) administration in two experiments. In Experiment I, 12 mares (six DEX, six control) were tested for sexual behavior in harem groups (two DEX and two control mares plus one stallion per group) for 9 consecutive days. In Experiment II, estradiol (E2) was given to a group of DEX-treated mares as an additional control. Twelve mares (four DEX, four DEX + E2, and four control) were tested in harem groups (one DEX, one DEX + E2, and one control mare plus one stallion per group) for 10 days. All DEX mares showed a clear suppression of sexual response compared to control or DEX + E2 mares, indicating that the estrous behavior seen in ovariectomized mares may be due to steroids from the adrenal cortex. The control and DEX + E2 mares were similar in all measures of proceptivity. Despite being more receptive, as indicated by fewer negative responses, the DEX + E2 mares received fewer intromissions and ejaculations than did the control animals. The ability of estradiol to induce estrous behavior in the dexamethasone-suppressed mare notwithstanding, other adrenal steroids, e.g., androgens, may be involved in estrous behavior in the untreated, ovariectomized mare.

Abstract: Ten ovariectomized (OVEX) and ten intact, but seasonally anovulatory (ANOV), pony mares were observed for sexual activity with five stallions, using a “harem group” social testing paradigm (two OVEX and two ANOV mares plus one stallion per group) for 15 consecutive daily tests lasting 20 min each. All mares in both conditions showed proceptive behavior in at least one test, all mares but one were mounted, and 14 of 20 mares received ejaculations. No statistical differences were found between the two conditions for any measure of proceptivity, copulatory activity, or days in estrus. The quality of estrus was judged to be equivalent to that displayed by periovulatory mares during their initial and terminal days of estrus, but less intense than that seen near ovulation. Mares in both groups were in estrus during approximately 60-70% of the tests and only 3 of the 20 mares were sexually refractory for more than five consecutive tests. Thus, the typical 2-week phase of sexual refractoriness seen in intact diestrous mares was absent in OVEX and ANOV mares, suggesting that the ovary plays a major role in actively suppressing estrous responses during the luteal phase of the cycle.