Horses grazing forest grassland in Sweden were found to increase pasture nutrient diversity and quality when compared with monthly mowing.
The two-and-a-half-year study showed that horse grazing diversified pasture chemical composition to a greater extent than mowing.
The results were achieved in an area thought to be suitable for the reintroduction of horses to the wild.
“This indicates that horses can manage pasture and are therefore suitable for year-round grazing in Sweden as a means to increase pasture diversity,” Sara Ringmark and her colleagues reported in the open-access journal Animals.
It is believed to be the first study at Nordic latitudes to evaluate the effect on pasture chemical composition of year-round grazing by horses without supplementary feeding.
Year-round grazing by cattle, sheep and horses is common in many European countries, but not in Sweden.
Reasons for this include a comparatively short growing season, the need for shelter to meet animal welfare legislation, poor winter growth, and the expected low nutrient content of pasture during the cooler months.
For their study, Ringmark, Anna Skarin and Anna Jansson, all with the Swedish University of Agricultural Sciences, examined the effects on pasture nutrient composition of 12 one-year-old Gotlandsruss stallions.
The Gotlandsruss is a native Swedish horse breed that has been present on the island of Gotland for centuries.
The young horses were kept in groups of four in three enclosures in Krusenberg, Uppsala, for two and a half years without supplementary feeding. The groups were rotated among the three enclosures for each growing season, which left all three enclosures having been grazed continuously for the full period of the study.
The enclosures – 13, 11, and 10 hectares – comprised roughly one-third fields and two-thirds forest. Water was offered in automatic troughs, but was also available in streams in the forest, even during winter. A salt block was provided in all enclosures, and the horses were wormed.
Each enclosure contained three areas in which the pasture was not grazed, but mowed monthly.
Samples of pasture were taken regularly for analysis, as were fresh fecal samples.
The study team found that the horse grazing increased the diversity of pasture nutrients when compared to the mowed areas. “Moreover, energy and protein concentrations and grass availability increased in areas grazed by horses, but decreased where grass was mown.”
This indicated that year-round grazing can be used to increase biodiversity, they said – a suggestion that was supported by botanical observations.
“The nutrient content in horses’ droppings was found to correlate with nutrient content in pasture, so analysis of droppings may be used to roughly estimate the quality of pasture consumed by horses.”
They continued: “Under the conditions studied, pasture protein content was sufficient to meet horse requirements year-round, while energy content and pasture availability may have been limited in winter.”
The authors noted that pasture quantity decreased over the study years in both the enclosures and the horse-excluded mown areas.
“This may, therefore, be an effect of annual variation, rather than an effect of horse grazing, on pasture production.
“To evaluate the long-term impact of horse grazing on pasture production, much longer studies are required.”
Ringmark, S; Skarin, A; Jansson, A. Impact of Year-Round Grazing by Horses on Pasture Nutrient Dynamics and the Correlation with Pasture Nutrient Content and Fecal Nutrient Composition. Animals 2019, 9, 500.