Abstract: The behavioral effects of the immunocontraceptive agent porcine zona pellucida (PZP) have not been adequately studied. Important managerial decisions for several species, including the wild horse (Equus caballus), have been based on this limited research. We studied 30 horses on Shackleford Banks, North Carolina, USA to determine the effects of PZP contraception on female fidelity to the harem male. We examined two classes of females: contracepts, recipients of the PZP vaccine (n = 22); and controls, females that have never received PZP (n = 8). We conducted the study during the non-breeding season from December 2005 to February 2006, totaling 102.2 h of observation. Contracepted mares changed groups more often than control mares (P = 0.04). Contracepts also visited more harem groups than did control mares (P = 0.02) and exhibited more reproductive interest (P = 0.05). For both contracepted and control females, the number of group changes (P = 0.01) and number of groups visited (P = 0.003) decreased with the proportion of years mares were pregnant. Our study shows that the application of PZP has significant consequences for the social behavior of Shackleford Banks horses. In gregarious species such as the horse, PZP application may disrupt social ties among individuals and inhibit normal social functioning at the population level.

Abstract: The evaluation of important parameters for measuring the horses’ cognitive capacities is one of the central topics of the equine behaviour team at Nürtingen-Geislingen University. Social complexity has been said to be one of the settings in which needs for cognitive capacities arise in animals. A variety of studies throughout the last two decades proved the horses’ social complexity to be far more elaborate than previously assumed. Horses form social bonds for the protection of offspring, intervene in encounters of others, identify group mates individually and easily orientate in a fission fusion society.
In such socially complex societies, animals will benefit from learning socially. In many bird and primate species the degree of social complexity correlates nicely with the species abilities for social learning. Social learning was, therefore, argued to be an indicator for elaborate mental capacities in animals. We were delighted to prove that horses actually copy social behaviour and techniques for operating a feeding apparatus from older and higher ranking group members. In a recent study we found young horses, at the age of 3 to 12, to copy the operation of a feeding apparatus from a human demonstrator. Social learning seems to work nicely in horses when the social background of the animals is considered.
The degree to which individual animals adapt to changes in their social or physical environment by finding innovative solution appears to be the other side of the coin, of whether animals adjust to challenges by social learning. It is not very astonishing, that along with the animals’ social complexity and their ability to learn socially also the degree to which they show innovative behaviour was claimed to be one of the most important demonstrations of advanced cognitive capacities. In a recent approach, we started to ask horse owners and horse keepers in many countries to tell us about unusual behaviour of their horses via a web site (http://innovative-behaviour.org). To date, we received 204 cases of innovative behaviour descriptions from which six cases were clear examples of tool use or borderline tool use. We categorized the innovative behaviours into the classes, a) innovations to gain food, b) innovations to gain freedom, c) social innovations, d) innovations to increase maintenance, and e) innovations that could not be clearly assigned to a category. About 20% of the innovative horses showed more than one innovation. These animals could be termed “true innovators”. Again, young horses were more innovative than older ones with the age group 5 – 9 showing the highest number of innovative behaviour descriptions.
In a nutshell, the horses’ cognitive capacities appear to be underestimated throughout the last decades. The horses’ social complexity is far more elaborate than previously assumed, horses learn socially from conspecific and humans, some of them demonstrate innovative behaviour adaptations to their environment and even simple forms of tool use.

Abstract: Third-party interventions are defined as the interruption of dyadic interactions by third animals through direct physical contact, interposing or threats. Previous studies focused on the analysis of interventions against agonistic encounters. However, there have been no evaluations of interventions against affiliative behaviours, particularly in relation to the intervening animal�s social relationships and its social and spatial position. Horses, Equus caballus, are an interesting model species, as interventions against affiliative interactions occur more frequently than against agonistic interactions. In this study, 64 feral horses displayed 67 interventions in affiliative interactions and eight interventions in agonistic interactions within the observation period. We analysed the interventions in affiliative encounters, and found that it was mainly higher-ranking females that intervened in the affiliative interactions of group mates in the stable horse harems. The intervening animals took an active part in affiliative and agonistic encounters within the group, but did not occupy particular social roles or spatial positions. They intervened in affiliative interactions in which group mates with which they had social bonds interacted with other members of the group. They targeted the nonbonded animal and approached the one with which they were socially bonded. We suggest some species use third-party interventions in affiliative interactions to prevent competition for preferred social interaction partners from escalating into more costly agonistic encounters.

Abstract: To date, a large amount of equine genetic data has been obtained regarding (i) extant domestic horses of various breeds from all over the world, (ii) ancient domestic horses, (iii) the extant Przewalski's wild horse, and (iv) the late Pleistocene wild horse from Eurasia and North America. Here, a review of mtDNA and Y chromosome marker analyses is presented in the context of horse domestication. High matrilineal (mtDNA) diversity, which can be found in both extant and ancient (domestic and wild) horses, has suggested that a high number of wild (and tamed) mares were domesticated. Alternatively, Y chromosome marker analysis revealed a single haplotype in all domestic horses analyzed; interestingly even a small population of extant Przewalski's wild horses showed two different Y chromosome haplotypes. It seems that an extreme male population bottleneck occurred due to domestication, while reduction in the female population was only moderate, leaving about 100 distinct haplotypes. For this reason, we speculate that domestication might have started when the appropriate stallion was found or was obtained by selection. Perhaps it had some unusual but special characteristics which could have accelerated the process of domestication. We doubt that only a single Y chromosome haplotype will be found in present-day domestic horses if there are no important differences between the founder stallion/s and the other stallions that were not included in the domestication. In the Eneolithic, tamed and wild mares have probably been spread all over Eurasia, although the number of animals was most likely very low and the populations were limited to a restricted area (e.g., taming centers). Only two subspecies of wild horses (Tarpan and Przewalski's wild horse) have survived up to recently. During the further process of domestication, mares (tamed or wild) were preferentially crossed to stallions having more desirable characteristics. We assume that mares from different regions varied in their morphology due to adaptation to their local environmental conditions. These data might explain rapid expansion of horse populations, as well as their rapid differentiation into various phenotypes during the early phase of domestication.