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 and 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 might be expected from agriculturally improved and intensively managed grasslands. Unfertilized species-rich grasslands had lower growth rates, reflecting low nutrient availability in spring and early summer. Low soil phosphorus 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 grasslands were 20%, or more, below values for conserved forages from intensively managed grassland. When losses incurred during the hay-making process were taken into account, then the nitrogen content of hays from many semi-natural grasslands appear to be sub-optimal for productive livestock. Metabolizable energy values of herbage cut for hay were 10-40% below values for intensively managed conserved grass. Phosphorus content of forages from most species-rich grasslands was either below the metabolic requirement of livestock or inadequate to sustain high individual animal performance. Potential problems associated with supplementation of the diet with phosphorus, and with high calcium-to-phosphorus ratios, are discussed. Although potassium content of most of the herbage cut for hay was adequate for productive ruminant livestock, exceptions arise with hay cut after July. The magnesium content of cut herbage from some semi-natural grasslands was below an adequate level for productive livestock. Most cut herbage appeared to contain adequate amounts of sodium. Inadequacy of the mineral content of hays from semi-natural grasslands for ruminant livestock will be exacerbated by nutrient losses incurred during the hay-making process and particularly so when hay-making 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 difficult to plan any integrated use of these hays in ruminant feed budgets for livestock systems.