Data from: Impacts of proactive health management on cattle and horse diets and dung biodiversity in Danish rewilding areas

Reintroducing megafauna to reinstate missing top-down trophic interactions
(trophic rewilding) is increasingly being applied as a tool to promote
self-regulating, biodiverse ecosystems. Even though the theoretical
background is clear, and megafauna effects are documented from prehistoric
ecosystems, the effects of reintroduced herbivores in contemporary
ecosystems remain understudied. This includes how reintroduced megafauna
interact with each other and the ecosystem, but also how current
management practices affect the processes they provide. In this
study, we investigated the effects of proactive health management, i.e.,
winter feeding and anti-parasitic treatments, on the ecosystem by
examining diets of large herbivores and dung-associated invertebrate
communities. We used environmental DNA metabarcoding to yield community
compositions of plants and invertebrates in dung from cattle and horses
from five comparable nature sites in Denmark, which differed in
management, and site/population-specific properties such as availability
of woody plant species, herbivore densities, and provision of winter
feeding and anti-parasitic treatments. We found different diet
compositions between cattle and horses, highlighting their functional
differences. For example, horse samples had higher relative read
abundances of graminoid and tree DNA. Supplementary feeding affected
diets, by decreasing consumption of graminoids and tree species relative
to forbs and legumes, probably originating from fodder, and intense
feeding seemed to almost eliminate consumption of local vegetation.
However, more studies are needed to generalize these findings. Several
invertebrate families were associated with either cattle or horse dung,
suggesting complementary effects on dung-associated invertebrate
biodiversity by these large grazers. The taxa that responded negatively to
anti-parasitic treatments were mainly parasitic nematodes (e.g., the
families Ancylostomatidae, Cooperidae, and Strongylidae), suggesting that
the applied treatments work as intended, but these results should be
interpreted with caution due to methodological limitations. Synthesis and
application. Our findings demonstrate functional differences between
cattle and horses, which suggest complementary effects on vegetation
development and consequently biodiversity. Also, our results indicate that
this functionality is impacted by proactive health management actions. We
suggest that potential effects on herbivory and biodiversity are carefully
considered before supplementary feeding or anti-veterinary treatments are
provided in year-round grazing systems and avoided if possible.