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Kimura, R. (2001). Volatile substances in feces, urine and urine-marked feces of feral horses. Can. J. Anim. Sci., 81(3), 411–420.
Abstract: The identity and amount of volatile substances in the feces, urine and feces scent-marked with urine (i.e., feces mixed with urine) of feral horses was determined by acid/steam distillation and gas chromatography-mass spectrometry. The frequency of excretion and scent marking, as evaluated in the breeding and non-breeding seasons, showed clear evidence of seasonal behavioral differences. The concentration of each substance (fatty acids, alcohols, aldehydes, phenols, amines and alkanes) in the feces differed according to maturity, sex and stage in the reproductive process. They had a characteristic chemical fingerprint. Although the levels of tetradecanoic and hexadecanoic acids in the feces of estrous mares were significantly higher than the respective levels in the feces of non-estrous mares, in the case of scent-marked feces by stallions, the levels of them in the feces from estrous mares had decreased to levels similar to those in non-estrous mares. The concentration of these substances in mares were not significantly different. The presence of a high concentration of cresols in the urine of stallions in the breeding season suggests that one role of scent marking by stallions is masking the odor of the feces produced by mares.
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Kimura, R. (1998). Mutual grooming and preferred associate relationships in a band of free-ranging horses. Appl. Anim. Behav. Sci., 59(4), 265–276.
Abstract: Preferred associate (nearest neighbour) and mutual grooming relationships among mares, in an isolated family band of free-ranging horses (Equus caballus), were studied, and the structural and functional differences between these two relationships were examined. The frequent partners accompanying the mare were not the same in both these relationships (p<0.05) and mares changed their partners during the study period between 1988-1990. Individual horses of similar rank tended to remain closer together in both winter and summer. Aggressive-submissive behaviour was so infrequent during spring that rank determinations could not be made; however, in fall, although rank could be determined, rank was not correlated with nearest neighbour. Three subgroups, based on preferred associate relationships in summer, fall and winter, directly reflected the age and social rank of the mares in the group. Individual horses of higher rank tended to have many partners in winter, while individuals of lower rank had fewer. There was no significant correlation between the frequency of mutual grooming and individual rank. The mutual grooming relationship was strongly influenced by seasonal changes as the relative amount of grazing time per day increased. Thus, the frequency of mutual grooming was lowest in winter and highest in summer. The mutual grooming relationship was based on the bonds between individual horses, which were little influenced by social rank. Lower ranking individuals tended to have a greater variety of grooming partners in summer.
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