To help plan conservation of the endangered Miyako horse, a biological resource of the Miyako Islands in Japan, we characterized the genetics of the breed by genotyping 32 microsatellites and identifying mitochondrial DNA haplotypes. We also calculated genetic distances between individuals based on the proportion of shared alleles and visualized the genetic relationships with a phylogenetic tree. Two important results were obtained. One is that accurate pedigree registration of the horse by using microsatellites is possible, as the exclusion power of parentage testing is 0.999998. Another is that the current genetic diversity of the horses was clarified. The average number of alleles, observed heterozygosity and expected heterozygosity were 4.2, 0.701 and 0.649, respectively, for the 35 analyzed horses. The probability values for bottleneck models (infinite allele model: 0.00000; stepwise mutation model: 0.00026; and two-phase model: 0.00000) suggested that Miyako horses have experienced a recent genetic bottleneck. Only one mitochondrial haplotype was identified. Consequently, genetic diversity within the population is relatively well-maintained despite a very small population size (41 at the time of the study), and the first priority in conservation of the Miyako horse is to increase the population size.

Thirty-two microsatellites and a mitochondrial DNA haplotypes of endangered Yonaguni horses were analyzed to establish a pedigree registration system and to understand their genetic diversity for planning effective conservation. Blood samples were collected from 78 of the 130 horses in existence, and DNA was extracted and genotyped. There were two major findings. One is that it is possible to use microsatellites for Yonaguni horse pedigree registration in the future because the power of exclusion of parentage testing is reliable at 0.999998. The second is the clarification of the current genetic diversity of Yonaguni horses. The average number of alleles, observed heterozygosity, expected heterozygosity and fixation index were 4.4, 0.591, 0.601 and 0.016, respectively, for the analyzed horses. The probability of a genetic bottleneck, under the assumptions of the stepwise mutation model, was 0.432, suggesting that the genetic structure of the horses was not influenced by a recent bottleneck. Genetic distance between individuals was visualized by a phylogenetic tree based on the proportion of shared alleles. Structure analysis based on Bayesian clustering revealed the possibility that Yonaguni horses comprise four or five subpopulations. Consequently, although only two haplotypes were identified in the mitochondrial analysis, genetic diversity of Yonaguni horses was not particularly low in comparison with that of other breeds that are at risk of extinction.

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Magnetic resonance imaging (MRI) is suggested to be useful for counting follicles and confirming ovulation in microminipigs. However, its accuracy is unknown. We have compared the number of follicles counted by MRI to that of corpus hemorrhagicum confirmed directly by visual inspection. The follicles of 17 microminipigs were counted by using ovarian MRI on a 0.4 Tesla MRI System every 24 hr after estrus until follicle images disappeared. Then, we performed laparotomy to count their corpus hemorrhagicum. Significant correlation was observed between follicle counts obtained using MRI (5.18 ± 1.78 per head) and the numbers of corpus hemorrhagicum (5.47 ± 1.74 per head). In conclusion, follicle counts using 0.4-T MRI were reliable, and confirmed microminipig ovulation.

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