Abstract: Although horses have laterally-placed eyes, there is substantial binocular overlap, allowing for the possibility that these animals have stereopsis. In the first experiment of the present study we measured local stereopsis by obtaining monocular and binocular depth thresholds for renal depth stimuli. On all measures, the horses' binocular performance was superior to their monocular. When depth thresholds were obtained, binocular thresholds were several times superior to those obtained monocularly, suggesting that the animals could use stereoscopic information when it was available. The binocular thresholds averaged about 15 min arc. In the second experiment we obtained evidence for the presence of global stereopsis by testing the animals' ability to discriminate between random-dot stereograms with and without consistent disparity information. When presented with such stimuli they showed a strong preference for the cyclopean equivalent of the positive stimulus with the real depth. These results provide the first behavioral demonstration of a full range of stereoscopic skills in a lateral-eyed mammal.

Abstract: OBJECTIVE: To estimate spatial risks associated with mare reproductive loss syndrome (MRLS) during 2001 among horses in a specific study population and partition the herd effects into those attributable to herd location and those that were spatially random and likely attributable to herd management. Animals-Pregnant broodmares from 62 farms in 7 counties in central Kentucky. PROCEDURE: Veterinarians provided the 2001 abortion incidence proportions for each farm included in the study. Farms were georeferenced and data were analyzed by use of a fully Bayesian risk-mapping technique. RESULTS: Large farm-to-farm variation in MRLS incidence proportions was identified. The farm-to-farm variation was largely attributed to spatial location rather than to spatially random herd effects. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that there are considerable data to support an ecologic cause and potential ecologic risk factors for MRLS. Veterinary practitioners with more detailed knowledge of the ecology in the 7 counties in Kentucky that were investigated may provide additional data that would assist in the deduction of the causal factor of MRLS via informal geographic information systems analyses and suggest factors for inclusion in further investigations.

Abstract: It is advantageous to identify individuals who are likely to behave fairly and those who are not. This ability to judge others’ fairness seems important for social species to interact or cooperate with their partners. Domestic horses (Equus caballus) have lived with humans for over five thousand years, hence they might have developed sensitivity to human personality. In the present study, we investigated whether horses would discriminate between a person who behaved fairly and a person who behaved unfairly. Specifically, we asked whether horses show a preference for the former. We tested 12 horses (11 thoroughbred and 1 Anglo-Arabian horses) at the horseback-riding club of Kyoto University. They were divided into 6 pairs which consisted of a participant and a partner. A participant was picketed between two polls next to a partner at the hoof washing place. Each horse put his/her mouth in an actor’s hand when the actor (an unfamiliar person) stood in front of them, and then received food from the actor. A fair actor always behaved fairly and gave a small quantity of hay (low-value food) to both of them in return for the task. An unfair actor always behaved unfairly, giving a small quantity of hay to the participant in return for the task, but always giving a piece of carrot (high-value food) to the partner in return for the task. Both actors always stood in front of the partner first, so the partner always did the task and received food from the actor before the participant. Finally, the participant was offered a piece of carrot by the two actors. The participant indicated which offer was accepted by stretching toward the chosen actor. The latter then moved the hand forward to allow the participant to take the food while the other actor’s hand withdrew. The orders (1st or 2nd) and the positions (left or right) of the two actors varied pseudo-randomly across trials. The color of the clothes of the two actors (white or black) was counterbalanced between sessions. We conducted 8 sessions, consisting of 8 experimental trials, across which the actors maintained their respective roles (fair or unfair) of the fair and unfair person. Furthermore, the two actors switched roles across sessions so that they played both roles the same number of times. One session was run per day. If horses can discriminate between fair and unfair people and show a preference for the former, they should choose the former significantly more often than the latter when both actors offered food. The participants showed no overall preference for accepting food from either actor. However, three of six participants showed a side preference. The result of the present study suggests that horses are insensitive to humans’ fairness. Horses may not have expectations about fair treatment.

Abstract: The ecology of Rhodococcus (Corynebacterium) equi in soil was studied on a horse-breeding farm. R. equi was cultured from soil at a depth of 0, 10, and 20 cm on the six sites of the farm at monthly intervals for 10 months from March to December of 1983. The highest numbers of R. equi were found in the surface soil. The mean number of bacteria in soil samples at every depth increased remarkably from 0 or 10(2) to 10(4) colony-forming units (CFU) g-1 of soil in the middle of April, and later decreased gradually. R. equi inoculated into six soil exudate broths prepared from surface soils at separate sites yielded suspensions with different optical densities, indicating differences in growth. The distribution of serotypes in the soil was similar to that in the horses on the farm. These findings indicated that R. equi could multiply in the soil and flourish in the cycle existing between horses and their soil environment.