Comparative experiments were conducted to assess the effect o f individual stallions on the fertilizing ability o f the spermatozoa in in-vitro-matured and partially zona-removed (PZR) equine oocytes (Experiment 1), as well as the effect o f mare breeds for ovaries from which oocytes were collected (Experiment 2). Experiment 1: Spermatozoa from 3 fertile stallions (A: Thoroughbred, B: Crossbred, and C: Palomino) were separately frozen-thawed in 5% glycerol and washed by a 4530% discontinuous percoll-gradient. Aliquots of the sperm were incubated for 3 h at 38.5°c in Brackett and Oliphant (BO) medium containing 2.5 mM caffeine and then treated for 60 sec with 0.1μM calcium ionophore A23187. The sperm suspension was introduced into BO medium supplemented with 0.3% BSA where 6 to 10 PZR oocytes after 32 h maturation culture were placed, and the oocytes and spermatozoa were co-incubated for 20 h. There were significant differences among stallions in the fertilization rates with PZR oocytes (34.2, 72.2, and 100% in stallions A, B, and C, respectively; P<0.05). High frequencies of monospermy in the fertilized oocytes were observed in the stallions with low fertilization rates (76.9, 57. 7, and 22.0% in stallions A, B, and C, respectively), resulting in similar overall proportions o f monospermic fertilized zygotes (range 22.0 to 41.7%). Experiment 2: Using mixed semen from 2 stallions (Stallions A and B), spermatozoa were incubated with PZR oocytes which were derived from the mare ovaries o f di f ferent breeds (Draft and Light horse). No significant difference in fertilization rates was found between the mare breeds (Draft and Light horse, fertilization rates 50.0 and 52.6%; overall monospermic fertilization rates 40.5 and 42.1 %, respectively).

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Diurnal rhythms of the mean R-R interval and the coefficient of variation (CV) of R-R intervals in eleven young Thoroughbred horses (2-year-old) were examined by periodic analysis to see whether the periodicity of the rhythms change with growing and physical training. On the diurnal rhythm of the mean R-R interval, a single spectrum (14.5 hr-19.3 hr periodicity) was extracted and the power, amplitude and the middle estimating static of rhythm (MESOR) of this periodicity increased with growing and physical training. On the other hand, two periodicities (14.5 hr-15.8 hr and 5.6 hr-7.5 hr periodicity) were found in the diurnal rhythm of the R-R interval variability but no alteration with growing and physical training was recognized. This suggests that the diurnal rhythm of the mean R-R interval and that of the R-R interval variability are extracted and reflect the different factors affecting autonomic nervous activity. Monitoring the diurnal rhythm of the R-R interval, furthermore, may enable us to understand the progression of growing and physical training effects.

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Sequential changes in the heart rate (HR), cardiac output (GO) and arterial blood pressure (ABP) were compared in dorsally recumbent iso f lurane-anesthetized horses with and without dobutamine infusion. The mean ABP and GO in horses given dobutamine increased to 71.7 mmHg and 89.7 ml/kg/min, respectively, and were significantly higher than the values in the group not given dobutamine. And there were no signs o f arrhythmia in the dobutamine-treated group. The mean dobutamine administration rate was 0.86±0.3 jig/kg/mm. The results show that dobutamine infusion enhances cardiovascular function in dorsally recumbent horses anesthetized with iso f lurane.

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Morphometrical analysis of the cervical vertebrae of thoroughbred foals was performed by a principal component analysis method. Foals without any spinal ataxia, consisting o f 26 males (4-21 months of age) and 13 females (5-23 months of age), were used. The cervical vertebrae ( from C3 to C7) were collected from these foals and bone morphometry on 28 measurements in each vertebra was performed. As a result, the first, second and third principal components were considered as the size, shape and sex factor, respectively. The combination o f the first and second principal components discriminated each cervical vertebral site clearly. The characteristic relationship between the second principal component and age was defined.

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