How should one design and position straw feeders in group-housed horses? A case study on occupancy and agonistic interactions at straw feeders in a large group of horses

As group housing of horses can be associated with increased injury risk especially when there are limited resources, the aim of this study was to allow initial, scientifically based recommendations regarding the positioning and design of straw feeders. Data collection took place in a Hinrichs Innovation + Technik (HIT) active stable with 50 to 62 horses kept in one single group. Occupancy, feeding distances, prevalence of agonistic interactions (AIS) as well as the percentage of feeding disturbances at two different straw feeders were analysed. Equine behaviour was recorded for 6 h/day on 15 summer and 15 winter days. Using generalised linear mixed models, considering the fixed effects of feeder, a fresh straw supply and the interaction of observation day and time period delivered the best prediction for the number of feeding events/h and the prevalence of AIS/h. Here, both feeders differed (p < 0.05) with twice as many feeding events/h, but threefold more AIS/h respectively twice as many AIS/horse at the larger feeder, where conspecifics fed side by side. Sixty-five % of the AIS with low risk of injury and 92% of the AIS with high risk of injury led to feeding disturbances. The latter made up 25% of all AIS in total with no differences between both feeders. Feeding distances did not differ either. The horses tended to use only every third opening space when feeding simultaneously. This knowledge should be taken into account when making assumptions about the de facto animal:feeding place ratio and the design of straw feeders in the future. Moreover, regarding the smaller feeder, the horses preferred to feed simultaneously with the feeder edge between them, so that the actual animal distances were smaller. Additional research is needed to investigate, how feeding in rectangular position to each other influences threatening behaviour inside a feeder. In this study, a central positioning within a paddock was beneficial with respect to feeder usage, but disadvantageous regarding AIS and displacements. However, the investigation of further straw feeders and farms is essential to allow general statements, as the study also proves that many factors such as season and rank order stability potentially influence equine behaviour at straw feeders. Group-housed horses´ behaviour at straw feeders is studied. At two feeders occupancy and agonistic interactions were observed for 30 days. At least three feeder openings were necessary to deliver one feeding place. 25% of agonistic interactions were associated with a high injury risk. A central feeder positioning promotes occupancy, but also agonistic interactions.