Doñana National Park, located in the south of Spain, is a protected area with a diverse ecosystem. Marsh-, shrub- and grasslands are home for many species. It hosts the biggest population of the wild horse breed Retuerta. Part of the National Park is administerated by the EBD, Estación Biológica de Doñana and is called Reserva Biológica de Doñana. There the 100 wild horses have been studied well during the last years. Social sturcture, migration, habitat use and genetics have been studied. Until now, though ,no attention has been given to intestinal or external parasite loads of the Retuerta horse population. Internal parasites can greatly affect the well-being of horses via tissue damage, nutrient- and weight loss (Andersen et al., 2013). Ectoparasites have a more indirect influence on horses (King & Gurnell, 2010). They can force horses to avoid habitats of high-quality forage or distract them from feeding (King & Gurnell, 2010). In addition, blood-sucking insects can transmit diseases and infections (King & Gurnell, 2010). Overall, for rewilding translocations, parasites can greatly influence the success of the reintroduction and survival of translocated individuals. This is the motivation for my Master project study that will focus on examining the parasite load of the Retuerta horse population in la Reserva Biológica de Doñana.

It has been shown that parasite load differs highly between age groups, herd size and habitat in other populations of feral and wild horses (Rubenstein & Hohmann, 1989, Rubenstein). Therefore in my study, individual parasite load will be recorded to improve the understanding of the factors that influence parasite abundance. The Retuerta population provides a good study system because each horse can be identified, and because records of their age and history have been kept over the last years.

For estimating the internal parasite load, horse feces will be analysed. Feceal egg counting and cultivation of eggs will be done. Routine McMaster methodologies will be used to quantify the number of eggs per gram feces (EPG) (Lester & Matthews, 2014). The eggs of most species of intestinal parasites can be morphologically discriminated, but Strongylus vulgaris eggs have to be cultivated to larval stage to identify the species (Andersen et al., 2013). Even though there are some limitations using feceal egg counting, it is still the most applicable and cost-effective technique to estimate internal parasite load. (Andersen et al., 2013) The presence of eggs in feces only provides information about the presence of adult helminths in the intestinal lumen, not the migrating or encysted larvae. Moreover, egg output varies highly both between and in the same individual over time (Wood et al., 2012). Factors like herd size, age and season can cause such variations.

Feces will be collected repeatedly for identified individuals during a total of four months, split into two two-months periods. The first sampling period will take place between April and May, where much forage is available. The second one between September and October. In this period, high temperatures and little rainfall mean low vegetation growth and therefore low forage. By examining parasite loads in both periods, the effect of food availability on parasite load can be investigated. In addition, horse location and the number of horses they associate with (herd size) will be recorded. A population of dewormed Anglo-Arabian horses living in a similar habitat will be used as a control for the intestinal parasite load.

To examine ectoparasite load I will use horsefly traps and photo capture. Since the horses can´t be approached directly, this study will concentrate on recording harassment by flies and mosquitos. Traps will be set up in different habitats and daytimes both separately and in clusters for a specific time. In addition, close-up photographs will be taken repeatedly of individual horses to count settled-down flies on animals. Temperature, solar radiation, wind speed and the amount of comfort behaviour shown by the horses will be measured each time a sampling takes place. For measuring comfort behaviour horses will be videotyped. Horsefly traps can be modified with a layer of glue if shade of the trap´s cover would alter its efficiency in attracting ectoparasites. Flies and mosquitos cought by fly traps will be counted and morphologically identified to species level. Therefore differences in the number of flies and diversity can be distinguished. When combined and analysed, these data can be used to investigate the relationship between horse behaviour and ectoparasite load.

Furthermore, internal and external parasite loads will be related to the body mass score (BMS). Body mass score will be estimated visually. Analysis of the data will allow me to investigate if there is a correlation between high parasite load and poor body contidtion.