Emil S. Thomassen explains the recent diet study of rewilded cattle and horses, showing functional differences between the two species and reveals the impacts of management actions on this functionality as described in their latest research.
The use of DNA metabarcoding for herbivorous diet analysis is a promising tool, yielding high-resolution data on plant consumption. In a time, where nature restoration and conservation are of high priority, we need more data on different management approaches, and how they affect ecosystems. Using this approach, we show that horse and cattle diets differ functionally and can be affected by winter feeding in semi-natural areas, where year-round grazing with both species is applied to restore natural functions and biodiversity.
Background
Reintroductions of large herbivores to exert control of vegetation communities (an example of trophic rewilding) has gained wide support and is currently being implemented in many areas across the globe with varying levels of implementation. Due to societal- and legislative constraints, it is not possible to fully abandon management and let the animals live completely wild. To avoid starvation, feeding is often provided in winter, where food is scarce, and animals are sometimes treated with anti-parasitic compounds to increase animal welfare. However, these management actions may impose unintended, detrimental effects on the functionality of the herbivores as well as the biodiversity connected to their dung.
Our study and the results
To test this, we extracted DNA from 315 dung samples from cattle and horses in five areas in Denmark, which had different approaches to feeding and treatments – in two areas the animals were fed a little bit, in two areas no feeding was provided, and in one area the animals received high amounts of winter fodder.
Using the DNA data, we characterized the diet compositions of the animals and the communities of dung-visiting invertebrates and found large differences between cattle and horses. The anti-parasitic treatments mainly affected the main target: parasitic roundworms, but due to methodological limitations, we cannot rule out that other dung-associated arthropods were negatively affected as well. We also found indications of altered diets when feeding was provided, resulting in higher consumption of forbs and legumes, which probably origins from the fodder at the expense of woody plants. However, these results need validation over more study sites in setups were area-specific properties can be clearly disentangled from management effects before they can be fully generalized.
Implications for management of future trophic rewilding projects
We show that feeding has the potential to affect diets of reintroduced, herbivorous mammals, and consequently, feeding practices might create “unnatural” grazing pressures. The consequences of such could be reduced plant diversity, vegetation densification, and encroachment of trees and shrubs, as expansive species are favoured by reduced consumption in the winter period. In the worst cases, feeding may compromise some of the intended biodiversity-effects of rewilding initiatives. However, it is worth noting that we did not address vegetation development directly in this study but simply discussed it based on our diet results. We encourage future studies to investigate how the trajectories of vegetation communities depend on winter feeding in controlled settings, to validate our findings and increase our knowledge of rewilding outcomes, with benefit for future applications.
Based on our diet results, while taking a cautious approach, we recommend that proactive management actions such as provision of feeding and anti-parasitic treatments should be reduced as much as possible in full-year grazing projects. Importantly, this does not imply reduction of management but rather the contrary. We suggest that reactive actions designed to mimic missing ecological processes, such as predation, natural population dynamics and grazing behaviour should be applied wisely and timely to avoid animal welfare problems while circumventing the need for proactive actions. We believe this approach to management is essential for promoting natural processes in contemporary, rewilded ecosystems.
Read the full article “Impacts of proactive health management on cattle and horse diets and dung biodiversity in Danish rewilding areas” in Journal of Applied Ecology.
