Abstract
Horse grazing may benefit biodiversity, but the impact of year-round grazing on nutrient dynamics has not been evaluated previously. This study compared pasture quality in a forest-grassland landscape grazed year-round by horses with that in exclosed mown areas. Twelve Gotlandsruss stallions were kept without supplementary feeding in three enclosures (~0.35 horse/ha) outside Uppsala, Sweden, from May 2014 to September 2016. Each enclosure contained three mown exclosures, where grass sward samples were collected monthly and analyzed for chemical composition and vegetation density. Fecal grab samples were collected and analyzed for crude protein (CP) and organic matter (OM) content. There were no differences in exclosure pasture energy or CP content between enclosures (p > 0.05). In grazed areas, there were differences in grass energy and CP content (p > 0.05) between enclosures. During the three summers studied, energy and CP content increased in the enclosures, but decreased in the exclosures. By the end, biomass content/ha was greater in the enclosures than in the exclosures. Fecal OM and CP content showed moderate to strong correlations with pasture nutrient content (r = 0.3-0.8, p < 0.05). Thus, in contrast to monthly mowing, horse grazing diversified pasture chemical composition and increased its nutritive value.
Highlights
Year-round grazing by cattle, sheep, and horses is common in many European countries, but not in Sweden
The exclosure samples showed lower dry matter (DM) and higher crude protein (CP) and metabolizable energy (ME) contents than the forage and volume samples from the enclosures, but there was no difference in neutral detergent fiber (NDF) content (Table 2)
There was a significant interaction between sample type and time period for ME per kg organic matter (OM) and CP as a percentage of OM (p < 0.05), where ME and CP remained at a high concentration in the period May–September in the graze samples, while decreasing from August onwards in the other sample types
Summary
Year-round grazing by cattle, sheep, and horses is common in many European countries, but not in Sweden. The effects on pasture quality and quantity of keeping horses year-round on extensive grazing have not been evaluated previously in the Scandinavian countries. Reasons for this might include the comparatively short growing season, the need for shelter to meet animal welfare legislation, and expected low nutrient content of pasture during winter. A study on year-round grazing horses in France indicated that crude protein intake was very low six months per year, and that adult maintenance requirement was met only in April–September [2] This estimation was based on fecal analyses of crude protein and an observed positive correlation between dietary and fecal crude content
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