Hay production from lowland semi-natural grasslands: a review of implications for ruminant livestock systems

Data on total, seasonal and between-year variability in the productivity an d nutritional quality of cut forages obtained from a range of lowland semi- natural grasslands are reviewed. Dry-matter production, as hay, from unfertilized species-rich semi-natural grasslands ranged from less than 20% to about 80% of the production that mi ght be expected from agriculturally improved and intensively managed grassl ands. Unfertilized species-rich grasslands had lower growth rates, reflecti ng low nutrient availability in spring and early summer. Low soil phosphoru s availability appears to be a key factor allowing high species-richness to be maintained. The in vitro digestibilities of herbage cut for hay from semi-natural grass lands were 20%, or more, below values for conserved forages from intensivel y managed grassland. When losses incurred during the hay-making process wer e taken into account, then the nitrogen content of hays from many semi-natu ral grasslands appear to be sub-optimal for productive livestock. Metaboliz able energy values of herbage cut for hay were 10-40% below values for inte nsively managed conserved grass. Phosphorus content of forages from most sp ecies-rich grasslands was either below the metabolic requirement of livesto ck or inadequate to sustain high individual animal performance. Potential p roblems associated with supplementation of the diet with phosphorus, and wi th high calcium-to-phosphorus ratios, are discussed. Although potassium con tent of most of the herbage cut for hay was adequate for productive ruminan t livestock, exceptions arise with hay cut after July. The magnesium conten t of cut herbage from some semi-natural grasslands was below an adequate le vel for productive livestock. Most cut herbage appeared to contain adequate amounts of sodium. Inadequacy of the mineral content of hays from semi-nat ural grasslands for ruminant livestock will be exacerbated by nutrient loss es incurred during the hay-making process and particularly so when haymakin g is prolonged by wet weather. Few feeding studies using hays from semi-natural grasslands of high nature conservation interest have been conducted. Lack of such data makes it diffi cult to plan any integrated use of these hays in ruminant feed budgets for livestock systems.