Background: Serotonin receptors can be divided into seven different families with various subtypes. The serotonin 1A (5-HT1A) receptor is one of the most abundant subtypes in animal brains. The expression of 5-HT1A receptors in the brain has been reported in various animals but has not been studied in horses. The 5-HT1A receptor functions related to emotions and behaviors, thus it is important to understand the functional effects and distribution of 5-HT1A receptors in horses to better understand horse behavior and its associated mechanism. Methods: Brain samples from seven different regions, which were the frontal, central, and posterior cerebral cortices, cerebellar cortex and medulla, thalamus, and hypothalamus, were collected from six horses. Western blot analysis was performed to validate the cross-reactivity of rabbit anti-5-HT1A receptor antibody in horse samples. Immunofluorescence was performed to evaluate the localization of 5-HT1A receptors in the brains. Results: The protein bands of 5-HT1A receptor appeared at approximately 50 kDa in the frontal, central, and posterior cerebral cortices, cerebellar cortex, thalamus, and hypothalamus. In contrast, no band was observed in the cerebellar medulla. Immunofluorescence analysis showed that the cytoplasm of neurons in the cerebral cortices, thalamus, and hypothalamus were immunostained for 5-HT1A receptors. In the cerebellar cortex, 5-HT1A was localized in the cytoplasm of Purkinje cells. Conclusions: In conclusion, the study suggests that 5-HT and 5-HT1A receptor systems may play important roles in the central nervous system of horses, based on the widespread distribution of the receptors in the horse brain.

Olfactory receptors (OR) are primarily responsible for the detection of odorant molecules. We previously demonstrated that OR7D4, an OR for androstenone, is expressed in the vomeronasal organ and olfactory epithelium tissue of stallions. Recently, the expression of OR1I1 in the human testes was reported and the possible roles of OR1I1 in the testicular cells were suggested. The objectives of this study were 1) to explore the expression of OR7D4 and OR1I1 in stallion testes, and 2) to define the specific localization of OR7D4 and OR1I1 in the testicular tissues. Stallion testicular tissue samples were used for this study. Western blot was performed to confirm the cross-reactivity of OR7D4 and OR1I1 antibody with stallion testicular tissue samples. OR7D4 and OR1I1 gene expressions were investigated using reverse transcriptionpolymerase chain reaction (RT-PCR) in stallion testes. Immunofluorescence was performed to investigate the expression of OR7D4 and OR1I1 in stallion testicular tissues. The protein bands for OR7D4 and OR1I1 from the testes were observed at approximately 38 kDa and 43 kDa, respectively. The mRNA of OR7D4 and OR1I1 were detected in stallion testes. Immunolabeling of OR7D4 and OR1I1 in the cytoplasm of both spermatogonia and Leydig cells was observed. In conclusion, androstenone and another odorant chemical, which is recognized by OR1I1, may play an important role in stallion testes.

In horse management, the alarm system with sensors in the foaling period enables the breeder can appropriately prepare the time of the parturition. It is important to prevent losses by unpredictable parturition because there are several high risks such as dystocia and the death of foals and mares during foaling. However, unlike analysis in the alarm system that detects specific motions has been widely performed, analysis of classification following specific behavior patterns or number needs to be more organized. Thus, the objective of this study is to classify signs of the specific behaviors of the mares for the prediction of pre-foaling behaviors. Five Thoroughbred mares (9-20 yrs) were randomly selected for observation of the prefoaling behaviors. The behaviors were monitored for 90 min that was divided into three different periods as 1) from -90 to -60 min, 2) from -60 to -30 min, 3) from -30 min to the time for the discharge of the amniotic fluid, respectively. The behaviors were divided into two different categories as state and frequent behaviors and each specific behavioral pattern for classification was individually described. In the state behaviors, the number of mares in the standing of the foaling group (3.17 ± 0.18b) at period 3 was significantly higher than the control group (1.67 ± 0.46a). In contrast, the number of the mares in the eating of the foaling group (1.17 ± 0.34b) at period 3 was significantly lower than the control group (3.33 ± 0.46a). In the frequent behaviors, the weaving of the foaling group was significantly higher than the control group, and looking at the belly of the foaling group was significantly lower than the control group. In period 2, defecation, weaving, and lowering the head of the foaling group were significantly higher than the control group, respectively. In period 3, sitting down and standing up, pawing, weaving, and lowering the head in the foaling group were also significantly higher than the control group. In conclusion, the behavior is significantly different in foaling periods, and the prediction of foaling may be feasible by the detection of the pre-foaling behaviors in the mares.

Advancing the estrous cycle of mares is an essential breeding strategy that is routinely conducted by Thoroughbred breeders to improve economic outcomes. For this purpose, Equilume light masks have been developed as an alternative to existing technologies such as artificial lighting or hormonal treatments because they are considered as valid as existing methods with additional animal welfare advantages. For example, with the Equilume light masks, horses can be let out into the pasture, whereas they have to be kept indoors during lighting treatment. Because the function of Equilume light mask on the estrous cycle of mares is influenced by environmental factors such as nutrition condition and temperature, Equilume light mask should be studied in various environments. The objective of the present study was thus to verify the effect of Equilume light masks on the onset of the estrous cycle in Thoroughbred mares in South Korea. Mares were randomly selected and separated into two groups at two Thoroughbred horse breeding farms. The mares in the treatment group were equipped with Equilume light masks from November 18 to February 10 the following year. The body condition, the number and size (> 35 mm) of uterine follicles, and the uterine horn score of the mares were assessed on January 6 and February 10. The body condition scores were not different between the two groups. The treatment with the Equilume light mask had no positive effects on developing follicles and the reproductive tract. In conclusion, the use of Equilume light masks did not influence the seasonal resumption of the estrus cycles in Thoroughbred mares in South Korea.

The conformational characteristics and performance of the horse breed should be evaluated to establish the breeding goals for a riding horse breed. Halla horses are cross-bred from Thoroughbred horses and Jeju ponies. Halla horses have been bred for speed as racing horses in Jeju Island in South Korea. However, some horses have also been used for riding purposes. Thus, the main purpose of this study was to evaluate the characteristics of Halla horses for riding purposes, which can be used as a guideline to define the breeding goals of Halla horses. Therefore, we evaluated the athletic performance of Halla horses by analyzing 3-year records of dressage (from S-3 Class to F Class) and show-jumping competitions (from S-2 Class to G Class) held in South Korea. We also examined the conformational characteristics of 15 Halla horses and compared them with those of 15 Thoroughbred and 15 Warmblood horses. In the results of dressage competitions over 3 years, Halla horses were awarded in D Class dressage only. In contrast, in the show-jumping competition, Halla horses were awarded in the D, E, F, and G classes. Overall, most body parts measured were smaller than those of Thoroughbred and Warmblood horses. When the rate of body parts per the average height of each breed was compared, Halla horses showed a higher rate of head length, head perimeter, and lumbar back length and croup length. In contrast, Halla horses had a shorter neck length. Based on the results of horse competition and conformation analysis, it is concluded that Halla horses are suitable for youth show-jumping competitions and have the potential to be representative riding horses in South Korea.

Endocrine system of hormones is the critical factor for the development of testes. The levels of hormones are orchestrated by a positive or negative feedback system controlled by the hyphothalamic-pituitary-gonad axis. The aim of this study was to investigate the effect of unbalanced endocrine system induced by the hemi-castration on testicular development in stallions. Four Thoroughbred stallions (age ranging from 3 to 5 yr) were used in this study. To disturb endocrine system, hemicastration has been performed on the stallions. Several parameters including testicular weight, volume, germ cell population on the cross-sections of round tubule, and the area of seminiferous tubules of stallion testes collected at the 1st hemi-castration and the 2nd hemi-castration (about 1 year after 1st hemi-castration) were compared. Testosterone levels were compared for 3 weeks before, after 1st castration, and before 2nd castration using enzyme-linked immunosorbent assay (ELISA) analysis. Immunohistochemistry (IHC) procedure was conducted to compare germ cell populations between after 1st and 2nd castration using VASA antibody. The VASA positive cell population per a cross section of round seminiferous tubule was obtained by monitoring 100 tubules. Interestingly, the weight of testes obtained at 2nd hemi-castration (384±14 g) were significantly higher compared to that of testes collected at the 1st hemi-castration (288±34 g). The volume of testes (306±34 ml) collected at the 2nd hemi-castration was higher than that of testes (169±18 ml) collected at the 1st castration. In contrast, VASA positive germ cell population on the cross section of round tubule (124.9±12.4 vs 142.9±21.6) and the area of round tubule (124±9.7 vs 122.9±1.7 mm2) were not different after 1st castration and 2nd castration. the testosterone levels in the blood collected before, after 1st castration, and before 2nd castration were not significantly different. In conclusion, the hemi-castration induces testicular development to maintain the normal reproductive systems in stallions.

The efficiency of artificial insemination (AI) for horses remains unsatisfactory. It is mainly because each process of AI causes a detrimental effect on semen quality. To sustain quality of semen properly, several factors including libido of stallions and sperm damage during sperm processing and preservation should be considered. Stallions with decent libido produce a high ratio of sperm to seminal plasma in their ejaculates, which is the ideal semen composition for maintaining sperm quality. Thus, to maximize the fertility rate upon AI, stallions should be appropriately managed to enhance their libido. Seminal plasma should have a positive effect on horse fertility in the case of natural breeding, whereas the effects of seminal plasma on both sperm viability and quality in the context of AI remain controversial. Centrifugation of semen is performed during semen processing to remove seminal plasma and to isolate fine quality sperm from semen. However, the centrifugation process can also result in sperm loss and damage. To solve this problem, several different centrifugation techniques such as Cushion Fluid along with dual and single Androcoll-ETM were developed to minimize loss of sperm and to damage at the bottom of the pellet. Most recently, a new technique without centrifugation was developed with the purpose of separating sperm from semen. AI techniques have been advanced to deliver sperm to optimal region of female reproductive tract at perfect timing. Recombinant equine luteinizing hormone (reLH) and low dose insemination techniques have been developed to maximize both fertility rate and the efficiency of AI. Horse breeders should consider that the entire AI procedure should be optimized for each stallion due to variation in individual horses for a uniformed AI protocol.