This study was conducted in order to observe the changes in cellular association of seminiferous tubules from 16 to 24 weeks of age and to obtain the cycle and relative duration of the seminiferous epithelia from 28 to 44 weeks of age in Korean native dogs. The results were summarized as follows; 1. Gonocytes were seen at 16 weeks of age, however they were not observed as from 20 weeks of age. Both type A and type B-spermatogonia occurred from 20 weeks, while primary spermatocytes were found from 20 weeks. Secondary spermatocytes and spermatids appeared from 28 weeks. Spermatozoa were observed at first at 28 weeks of age. 2. Type A-spermatogonia appeared approximately 1.6 times as many at stage II compared to stage I, while the same numbers of cells were seen in both stage I and VII, showing the least number among VIII stages of the cycle of the seminiferous epithelia. The type B-spermatogonia were found from stage VI to VIII, Leptotene phase of the primary spermatocyte divided from type B-spermatogonia in stage VII observed at the stage VIII. Pachytene phase of the primary spermatocytes were shown the least in number at stage IV. The secondary spermatocyte could be seen only at stage IV. 3. The relative frequency of each stage from stage I to VIII of the cycle of the seminiferous epithelia was 30.3, 12.0, 9.8, 4.2, 8.5, 10.5, 11.4 and 13.4% respectively. Thus the establishment of spermatogenesis in Korean native dog was completed from 28 weeks of age.

The purpose of this study was to investigate the effect of antioxidants (vitamin E, selenium, and coenzyme $Q_{10}$) on the bleomycin-induced pulmonary lesions in male rats. Sprague-Dawley male rats were divided into 4 treatment groups ($T_1$, $T_2$, $T_3$, $T_4$) and 4 control groups ($C_1$, $C_1$, $C_3$, $C_4$). The treatment groups of rats weie given a single intratracheal dose of bleomycin (1.5 units/rat) and control groups of rats were given a single intratracheal dose of normal saline (0.15ml/rat). The rats in the $T_1$ group and $C_1$, group were dosed with normal saline (0.5ml/kg/day), the rats in the $T_2$ group and $C_2$ group were dosed with vitamin E (50mg/kg/day), the rats in the $T_3$ group and $C_3$ group were dosed with sodium selenite (3mg/kg/day) and the rats in the $T_4$ gronp and $C_4$ group were dosed with coenzyme $Q_{10}$ (2.5mg/kg/day) intraperitoneally for 7 days or 14 days, respectively. Animals were killed at 7th and 14th day after dosing with bleomycin or saline. The results obtained were as follows: 1. Lung wet weight of treatment groups of rats was increased significantly while body weight gain of them was decreased significantly in comparison with that of control groups of rats (p<0.01). 2. The ratio(%) of lung wet weight to final body weight of treatment groups of rats was increased significantly in comparison with that of control groups of rats (p<0.01). 3. The main histopathological findings of lungs observed in rats at 7th day after dosing with bleomycin were proliferation of the type II alveolar epithelial cells and fibroblasts, increased invading of macrophages into lesions, round cell infiltration and perivascular edema. 4. Lung fibrous tissues were markedly increased in rats observed at 14th day after dosing with bleomycin. 5. Pumonary lesions observed in rats dosed with bleomycin and antioxidants(vitamin E, selenium, coenzyme $Q_{10}$) were not significantly different from those of rats given bleomycin alone.

Deer hemal nodes were studied by gross anatomy and light microscopy. Hemal nodes were scattered in the periphery of thoracic and abdominal aortae, and spherical or avoid in shape. A hemal node consisted of a thin capsule and a hilum, and had numerous small subcapsular and deep sinuses distended by a great number of erythrocytes. Although a few lymphatic nodules and tissues were seen in the parenchyma, no typical cortex and medulla was defined. Blood vessels occurred, but lymph vessel was not observed in nodes. The parenchyma of the hemal node consisted of many erythrocytes and lymphocytes, and a few granulocytes, plasma cells megakaryocytes and macrophages. The stroma was composed of reticular cells and fibers. The capsule and trabecula was a collagenous connective tissue with smooth myofibers. The above findings suggest that the hemal nodes are involved in blood storage, blood filtration and immune reaction.

가토 적출 신동맥에 있어서 purinergic 신경 분포를 perivascular nerve stimulation을 통해서 확인하였다. 1. 가토 적출 신동맥은 perivascular nerve stimulation에 의해 수축성 반응을 나타내었다. 2. Perivascular nerve stimulation에 의한 수축현상은 자극의 크기와 자극의 빈도에 의존적이었으며, 내피세포의 유무에는 영향을 받지 않았다. 3. Perivascular nerve stimulation에 의한 수축현상은 prazosin$(1{\mu}M)$에 의해 강하게 억제되어졌으며, tetrodotoxin$(1{\mu}M)$ 또는 ${\alpha},{\beta}-methylene$ATP$(10{\mu}M)$에 의한 $P_{2x}-purinoceptor $ desensitization에 의해 완전히 수축현상이 사라졌다. 이와같은 결과는 가토 신동맥에는 purinergic신경이 분포되어 있으며, perivascular nerve stimulation에 의해 purinergic 신경전달물질이 norepinephrine과 함께 유리되어지는 것을 시사하고 있다.

The present experiments were undertaken to produce the standard antiserum for equine blood typing. The following results were obtained through ISO and Hetero Immunizations of the horses whose blood typing was analysed in the Laboratory of Racing Chemistry of Japan. 1. Of the 21 combinations of ISO-immune, 17 horses were produced antibody (about 80%) 2. Antibody titers were increased from early 1 week to late 5 weeks and any antibody titers were not be obtained in spite of the using of adjuvant and 10 repeated injections in the other 4 horses. 3. High antibody titers were obtained within the earliest period in the Dd antigen but were not increased over 32 times in spite of 8~10 repeated injections in the antigen. 4. Antibody were easily produced in the Ca antigen of ISO-Immune but production of antisera were tailed due to abscence of absorbed blood cell. 5. Antibody titers of 1,024 times were obtained through 5 injections in the Ca of HeteroImmune 6. Of the produced 15 antisera (16 system), 13 antigen (5 system) were absorbed.

Progesterone의 단크론성 항체를 생산, 이용하여 감도가 높으면서도 신속히 측정할 수 있는 ELISA 기법을 처음으로 개발코져 실시하였다. 단크론성 항체는 종래의 면역방법에 의해 획득한 항혈청에 비해 약 10배의 결합율을 보였고 titer 역시 높았다. Dot-blot 분석 결과 단크론성 항체는 IgM이었다. 경합반응은 2시간으로 충분하였고, progesterone 표준용액을 이용한 표준 곡선은 0~1000pg/well에서 거의 직선적이었다. Progesterone의 단크론성 항체를 이용한 ELISA는 임상적으로는 물론 연구용으로도 신속한 항체의 기능 측정에는 물론 각종 번식 관련의 지표로 충분히 활용될 수 있을 것으로 판단된다.

This study was carried out to investigate the amino acid and protein concentrations in amniotic fluid and the potency of the teratogenic effect of ethylenethiourea(2-imidazolidinethione, ETU) in the fetuses due to different dose amounts of this compound. The S.P.F. Sprague-Dawley female rats(10 weeks) were used in this study and these animals were divided into four groups; control group(25pregnant female rats), group I (dosed ETU from day 7 to day 17 of gestation at 10mg/kg/day), group II (dosed ETU from day 7 to day 17 of gestation at 30mg/kg/day), group III (dosed ETU from day 7 to day 17 of gestation at 50mg/kg/ day). 250mg/100mg ETU in group I, 750mg/100ml ETU in group II and 1,250mg/100ml ETU in group III were administered 4ml/kg 13.W by oral route. The results obtained were summarized as follows; 1. The anomalies of the external examination werf meningocele in the head, kinky tail, clubfoot and sharp tail.(Meningocele, in group III, significantly increased from control value at p<0.001). 2. The skeletal variations and delayed ossification were Lumbar ribs, asymmetric sternebrae, asymmetric 13th rib and delayed ossification of skull. Asymmetric sternebrae(group III ) was significantly increased from control value at p<0.05 and delayed ossification of skull (group II and III ) were significantly increased from control value at p<0.05 and p<0.01, respectively. 3. The internal soft tissue anomalies were hydroencephaly of 3th lateral ventricle, dilatation of ureter, dilatation of renal pelvis and cleft palate. (Hydroencephaly, 28.1% in group I, 88.3% in group II and 100% in group III ). 4. Protein values in amniotic fluids are not significantly decreased in 10mg/kg group but significantly(p<0.05) decreased in 30mg/kg group and 50mg/kg group from control group. 5. In the levels of amino acid in amniotic fluids, the levels of glntamic acid, iso-lencine, leucine, tyrosine and phenylalanine of 10mg/kg group are significantly decreased from control group. In 50mg/kg group, except for glycine, valine and methionine, all amino acid levels are significantly(p<0.05) decreased from control group.

This study was carried out to investigate; the alpha-fetoprotein, urea and free fatty acid in amniotic fluids and water filled multiple T-maze test of fetuses affected by Ethylenethiourea. The S.P.F. Sprague-Dawley female rats(10 weeks) were used in this study and these animals were divided into four groups; control group I (10mg/kg/day), group II(30mg/kg/day), group III(50mg/kg/day). The results obtained were summarized as follows; 1. In the water filled multiple T-maze test of F1 male rats, The time and errors from start point to goal point of 30mg/kg group are significantly(p<0.001) increased from control group in 3rd day of test. In F1 female rats of 2nd day and 3rd day of water filled multiple T-maze test, The time and some errors in 30mg/kg group are significantly (p<0.05) increased from control group. 2. Alpha-fetoprotein values of all treated groups(10mg/kg, 30mg/kg and 50mg/kg) were significantly(p<0.001) decreased from control values in the amniotic fluids. 3. Urea values of ammniotic fluids in 50mg/kg group are significantly increased from control group. 4. Free fatty acid values of ammniotic fluids in 50mg/kg group are significantly increased from control group.

Effects of recombinant bovine somatotropin$({\gamma}BST)$ on mineral composition of milk were investigated in Twenty-five multiparous Holstein dairy cows. Recombinant BST was administered by two different routes; intramusculary(12.5mg and 25mg/day) and subcutaneously (500mg and 750mg) in sustained-release vehicle every 2 weeks beginning 4 week postpartum and continuing for 7 months. Milks were collected 0,1,2,3,5 and 7 months after beginning of treatments in control and ${\gamma}BST$-administered groups. Mineral composition, such as Ca, Pi, Na, K, Mg, Zn, Fe and Mn, in milk were not affected by the administration of ${\gamma}BST$ regardless of dose and dosage forms. It is concluded from the observations of these experiments that the dose and dosage forms of ${\gamma}BST$ employed in this work might not affect milk mineral composition in dairy cows under the normal sanitary condition and adequate nutrient balance.

Guinea pigs were administrated with T-2 toxin at a rate of 1 and 0.6mg/kg body weight per day for 21 days to study the immunological and pathological effects of T-2 toxin in guinea pigs. Blood was collected before T-2 treatment and on days 7, 14 and 21 of the trial for hematological and biological examinations and for the mitogen assay using lymphocytes. Myeloid: erythroid ratios were examined from the fernur bone marrow samples taken a day before T-2 toxin treatment began, on day 12 and at death. Guinea pigs received with 1mg/kg body weight of T-2 toxin daily showed leukopenic, lymphopenic and anemic signs on day 7 and 14. The mitogenic responses to the T-cell mitogen, Concanavalin A and B-cell mitogens, lipopolysaccharide were significantly depressed on day 7. Histologically, marked cellular damages including karyorrhexis and depletion of lymphocytes were observed in the actively dividing cells of the gastrointestinal tract, lymph node, spleen and bone marrow of guinea pigs.

In this study, effect of levamisole, selenium and tocopherol on the lymphocyte blastogenesis and antibody production in Korean native goat were evaluated in vitro and in vivo. Lymphocyte blastogenesis of goat blood increased significantly (p<0.01 and p<0.05) when the cells were treated in vitro with levamisole at the concentration of $50{\sim}500{\mu}g/ml$, with selenium at the concentration of $0.062{\sim}1.0{\mu}g$ and with tocopherol nt the concentration on $12.5{\mu}g$. Increased lymphocyte blastogenesis was detected from 2 to 24 hours after oral administration of levamisole (2.5mg/kg of body weight). After 7 days, increased mitogenic response of lymphocytes was not detected. Meanwhile increased blastogenesis of lymphocyte from goats given the selenium-tocopherol mixture (selenium $100{\mu}g$-tocopherol 200IU/head/day) was detected from 10 days after feeding, and the tendency continued throughout the entire experimental period. When immune responses of goats against PPD were subjected to test by ELISA, the mean IgG titers of levamisolc group (1 : 1,800) and selenium-tocopherol group (1 : 960) were higher than that of control group (1 : 600) at 2 weeks after lst inoculation. At 3 weeks after lst inoculation and 1 week after 2nd inoculation, the significant (p<0.05) differences in IgG titers were detected among the three groups. The mean IgG titers of levamisole group, selenium-tocopherol group and control at that time were 1 : 20,480, 1 : 5,120 and 1 : 2,640, respectively. The IgG production of levamisole group was significantly (p<0.01) higher than that of control group.

The present study was conducted to investigate biochemical properties and antimicrobial drug susceptibilities of 57 strains of Pasteurella haemolytica (P haemolytica) isolated from pneumonic calves and goats in Youngnam province during the period from September 1989 to February 1991. P haemolytica was isolated from 95 of 142(31.7%) pneumonic calves of 1 to 6 months of age and from 9 of 24(37.5%) pneumonic goats of 2 to 10 months of age. Seasonal isolation frequency of P haemolytica in calves and goats varied from 16.6 to 35.7%, and it was higher in winter. The majority of biochemical and cultural properties of P haemolytica isolated from calves and goats were identical to those of the reference strains employed. All isolates were susceptible to ceftiofur, erythromycin, kanamycin, gentamicin, and chloramphenicol (MIC: <$25{\mu}g/ml$), some of them were resistant to amikacin, sulfadimethoxin, and streptomycin (MIC: >200IU or ${\mu}g/ml$).

Clinical and bacteriological observations on infectious atrophic rhinitis of swine were conducted in order to obtain some basic information for the clinical and immnnological control of the disease prevailing in the republic. Samples were collected from nasal cavities of 135 4~12 week old pigs from 12 herds and from turbinates of 199 slaughtering pigs from 14 swine herds to investigate the prevalence of Bordetella bronchiseptica and/or Pasteurella multocida in the nasal cavities of the pigs. On the examination of nasal swabs by cultural techniques and of gross lesion of snouts of slaughtering pigs, all the swine herds investigated were found to be affected by atrophic rhinitis and a total of 84 B bronchiseptica and 139 P multocida cultures were isolated from the nasal cavities of the pigs. Of the 199 slaughtering pigs, some 48% revealed gross pathological lesion typical of atrophic rhinitis and the prevalence of B bronchiseptica and P multocida were 27.6% and 46.7%, respectively. Biochemical properties, antimicrobial susceptibilities, serological characteristics and toxigenicity of the isolates of B bronchiseptica and P multocida were investigated.

Attempts to isolate chicken anemia agent (CAA) were made by inoculating tissue homogenates into MDCC-MSBl or LSCC-1104B1 cell lines and passaging the cells serially. CAA was isolated from the liver and thymus of 11 weeks old layer chickens and from the liver of 10 weeks old broiler breeder chickens. The layer flock experienced approximately 45% mortality during 9 to 14 week of age from gangrenous dermatitis and lymphoid organs of affected chickens were severely atrophied. The broiler breeder flock experienced approximately 7% mortality during 7 to 9 weeks of age and affected birds showed lesions of colibacillosis, staphylococcal arthritis, and coccidiosis together with atrophied lymphoid organs. The isolated viruses were identified as CAA by the indirect fluorescent antibody test and virus neutralization test using CAA immune sera including one to Gifu-1 strain of CAA. The CAA isolate 89-69, when inoculated into susceptible 1 day old SPF chicks, induced anemia 14 to 16 days after inoculation. It did not induce any cytopathic effects in chicken embryo liver and chicken embryo fibroblast cell cultures. Infectivity of the isolate was not affected by the treatment of chloroform or heat ($70^{\circ}C$ for 15 minutes).

Encephalomyocarditis(EMC) virus was isolated from the mummified and stillborn pigs at a swine farm in Chonnam Province, experienced with EMC infection over the period Oct.~Dec. of 1989. In addition some cultural, serological properties of the isolates and experimental infections in the piglets were studied. The results obtained were as follows; 1. Two EMC virus strains with HA titers and CPE similar to EMC-ATCC were established in a baby hamster kidney (BHK)-21 cell line by inoculating homogenates of brain and heart of the 19 mummified or stillborn pigs and designated $K_3$ and $K_{11}$. 2. At the second BHK-21 cell line passage of the initial isolates CPE appeared after incubation for 16~18 hours, while at the fourth and fifth passage the highest titer of HA was recorded, titer of HA using rat and guinea pig erythrocytes. 3. One pig inoculated with the isolate $K_3$ showed dyspnea as clinical signs and died at the 10 days after inoculation at necropsy white necrotic foci were observed from the dead animal heart. 4. Although all the rest surviving pigs showed increases in antibody titer and body temperature of $40^{\circ}C$ above for the initial 2~4 days followed by the return to normal, there were no gross lesions when the animals were sacrificed at the 2 weeks after inoculation.

A 7-year old Holstein bull showing marked thickening of left forelimb was diagnosed as pulmonary hypertrophic osteoarthropathy on the histological basis of the exostotic bone of left metacarphus. Thickening of the bone was due to apposition of excessive cancerous bone beneath the periosteum on the shaft. The lung lesion of the bull, chronic suppurative bronchopneumonia was possibly related to pathogenesis of the bone thickening.

This study was conducted to detect the serum antibodies in the experimentally toxoplasma infected dogs and street dogs by use the of an enzyme-linked immunosorbent assay (ELISA). And this test was performed on the polystylene microplate by coating with the tachyzoites soluble antigen of T gondii (RH strain), incubated with sera diluted then, added with HPO-conjugated rabbit anti-dog IgG and o-phenylenediamine used as a substrate. Tachyzoites of T gondii harvested from mouse peritoneal cavity were purified by 30, 40 and 50% Percoll density gradient centrifugation and used as the source of antigen. The results obtained were summarized as follows; 1. The highest ratio of positive to negative (P/N ratio) was obtained at the level of $l{\mu}g/ml$ protein concentration of antigen with the 1/4000 dilution of the conjugate measured by checker-board titration. It was regarded as the optimum concentration of the antigen and conjugate. 2. Cut-off value in this IgG ELISA was 0.375 that was determined by mean absorbance (at 492nm) of IFA negative serum added with the dauble value of the standard deviation $(mean{\pm}2S.D.)$. 3. Serum ELISA IgG antibodies to T gondii in the exyerimentally infected dogs were detected firstly at the Week 3 after inoculation and the highest titer was recognized at the Week 4, 5 and 6 after inoculation. 4. Stability of the antigen absorbed in the microplates that were preserved at $4^{\circ}C$ and $-25^{\circ}C$ separately were prolonged up to 3 weeks and 10 weeks at $4^{\circ}C$ and $-25^{\circ}C$, respectively. However the reproducibility was not reliable after the preservation of 4 weeks and longer. 5. Positive rate of the specific antibodies in 312 test sera was 28.5% and there was no significant differences between the male (27.8%) and female (29.5%), respectively. 6. The IgG ELISA was proved to be a specific procedure for the detection of antibodies to canine toxoplasma infection and also evaluated as a screening test for the large scale of test samples in laboratory.

Diagnosis of cryptosporidiosis is currently confirmed by the detection of the oocysts or endogenous stages in fecal or tissue samples. Various conventional staining methods and serodiagnostic techniques have been reported, but the latter has far been limited to a few laboratories. Cryptosporidium has recently been reported in mice and chiekens in Korea, but there has been no report on staining methods to the oocysts. The present study was performed by light and scanning electron microscopic observations, and discussed with staining properties of four conventional methods such as dichromate solution floatation method, Carbol fuchsin stain, Auramine-O stain and Giemsa stain method. Cryptosporidial oocysts were isolated from the laboratory mouse. In tissue sections of duodenum, jejunum, ileum, cecum and upper colon, numerous very small, basophilic bodies were observed on the border of mucosal epithelial cells. In scanning electron microscopic observations, a few of developmental stages of Cryptosporidium were seen. Two types of thick and thin-walled oocysts were recognized in the intestinal contents. Mean size of its were $5.19{\pm}0.23{\times}4.31{\pm}0.32{\mu}m$ and $5.14{\pm}0.25{\times}4.27{\pm}0.4{\mu}m$, respectively. Carbol fuchsin and Auramine-O stain methods are recommended as the satisfactory ones for the identification of Cryptosporidium oocysts. Giemsa stain was also recommended as available in the laboratory, because a few of developmental stage fo Cryptosporidium could be seen by it.

Preliminary survey on the prevalence of swine internal parasites was carried out at 91 pens of 4 piggeries being operated by the sawdust fermentation floor system in Kyunggi province. To investigate the effects of viability of eggs., larva and cysts, temperatures at the underlayer of the sawdust floor and rooms of pens were taken three times a day for 8 days. In a pig farm which has been operated by the sawdust fermentation floor system for G years, eggs and larva of Ascaris suum, Trichuris suis, Oesophagostomum sp., Hyostrongylus sp. and Strongyloides ransomi were detected from 42(70.0%) among 60 pens. Cysts and oocysts of coccidia, Balantidium coli, Entamoeba sp. were also detected from 50(83.3%) among 60 pens. In three pig farms which have been operated by the sawdust fermentation floor system for one year, eggs and larva of nematoda were not detected at all, and the contamination rates of protozoan cysts and oocysts was relatively low situation. The change of the temperature in the pig room was variable according to outside condition, whereas that in underfloor was consistently stable between $28^{\circ}C$ to $30^{\circ}C$ which was strictly suitable for the development of eggs, larva and cysts.

A field study of Lymnaea viridis, the intermediate host of Fasciola hepatica, was carried out in the eastern Chonnam area. The snail was distributed all over the place. Their major habitats were rice paddies (60.8%), followed by brooks (23.2%), irrigation canals (8.6%), and drains (5.6%). Other minor habitats included natural ponds (1.5%), lakes (0.4%), and rivers (0.1%). L. viridis was living in wet clay soil, occasionally entering water. The snails discharged egg masses when the temperature was $15{\sim}20^{\circ}C$, and the number of the snails was the highest late in October. At $9^{\circ}C$ the snails were not found on the mud: they were present deep in water or at the base of rice stubbles. These hibernation sites were discussed with the epidemiology of fascioliasis.

Pain reflex and anesthetic state in swine with xylazine epidural anesthesia were observed. In xylazine epidural anesthesia, dosages of 0.50mg/kg BW for analgesia of perineal region and 0.7550mg/kg for analgesia of low abdominal wall were required. Regional anesthesia was induced 5~20 min after epidural injection of xylazine and recovered 90~120 min after administration. The results indicated that xylazine as an epidural local anesthetic was useful in swine.

The effects of ethylene glycol, DMSO and glycerol as cryoprotectants and the effect of concentrations(0, 0.25, 0.5 and 1.0M) of sucrose in the diluent on the viability of the aggregated morulae frozen rapidly in liquid nitrogen$(LN_2)$ vapour were examined. The morulae were produced by aggregation of ICR and CBA mice embryos at 8-cell stage. Before freezing the embryos were equilibrated in 1.5M cryoprotectants+0.25M sucrose in oae-step or in 3.0M cryoprotectants+0.25M sucrose in two-steps. The embryos were pipetted into the freezing medium fraction of 0.25ml plastic straws. The straws were frozeu by directly transfer into $LN_2$ vapour(about lcm above $LN_2$) for 2 minutes, and then plunged into $LN_2$. After thawing the cryoprotectants were diluted with 0, 0.25, 0.5 or 1.0M sucrose solution. The post-thawed in vitro viability of the aggregated embryos was significantly dependent on the type and concentration of cryoprotectants in the freezing medium and also on the concentration of sucrose in the diluent. When the aggregated embryos were equilibrated in 1.5M cryoprotectants +0.25M sucrose in one-step and diluted with 0.5M sucrose after thawing, the survival rate of the embryo5 was significantly(p<0.05) higher in DMSO(62.5%) or ethylene glycol(52.2%) than in glycerol(33.3 %). In the case that the concentration of the cryoprotectants was raised to 3.0M in two-steps, thc higher survival rate of the embryos was obtained in ethylene glycol or glycerol than in DMSO followed by diluting them with 0.5 or 1.0M sucrose after thawing(p<0.01).

Plasma progesterone concentrations were measured from 97 Che-ju native mares throughout the estrous cycle, Day 20 to 23, 5 to7 months of pregnancy, and gestation period (<1 to 7 months) using the radioimmunoassay techniques for pregnancy diagnosis. Plasma progesterone concentrations during the estrous cycle were the lowest (<1.0ng/ml) at estrus, remained high from 9 to 18 days (3.7~7.6ng/ml) and drastically decreased thereafter to reach minimal concentrations at the next estrus. Plasma progesterone concentrations at Day 21 to 24 were a significantly different between in pregnant mares (>5.7ng/ml) and in non-pregnant mares (<1.0ng/ml). The accuracy of the pregnancy diagnosis based on plasma progesterone concentrations at Day 20 to 23 was 86.7% for positive and 100% for negative, whereas on 5 to 7 months was 66.7% for positive and 71.0% for negative, respectively. Plasma progesterone concentrations during the gestation period(1 to 7 months) increased after 1 month of pregnancy, with peak concentrations(>8.0ng/ml) occurring between 60 to 100 days of pregnancy, and decreased below 1.7ng/ml after 6 months of pregnancy.