Grazing and ensiling of energy-rich grasses with elevated sugar contents for the sustainable production of ruminant livestock (Acronym: SweetGrass)

Abstract

Permanent grassland dominates the Irish landscape and for many decades perennial ryegrasses have been the main constituent in seed mixtures for grassland. The main attractions in favour of perennial ryegrass swards are that they: x produce high yields in response to fertiliser nitrogen x have a high digestibility when harvested at the appropriate growth stage x are relatively easy to preserve as silage due to their superior content of sugar x persist as permanent swards where favourable management practices prevail If the phenotype of perennial ryegrass were to be improved, one potentially desirable trait would be an elevated concentration of water-soluble carbohydrates (WSC). This could confer benefits in terms of: x further increase the probability of achieving a lactic acid dominant fermentation during ensilage. This could reduce the requirement for traditional acid- or sugar-based additives, improve the likelihood of a positive response from additives based on homofermentative lactic acid bacteria or alternatively eliminate the need for any or the currently available conventional additive. If its effect was to improve silage preservation this should positively impact on dry matter (DM) recovery, improve animal productivity and potential product quality, and reduce N loss to the environment. x improve the opportunity to produce silage with an elevated concentration of WSC. In circumstances where little or no supplementary concentrate feedstuffs were offered with silage, higher residual WSC could enhance silage intake and digestion, thereby improving animal productivity and reducing urinary loss of N. x produce a grass with higher intake characteristics during grazing, resulting in improved or more efficient animal production. x better synchronise or balance the supply of a rapidly fermentable carbon source (e.g. WSC) with soluble N compounds in the rumen of cattle or sheep. This could be important with grazing animals in spring and particularly in autumn when grass N content can be relatively high. Improved synchronisation or balance could potentially improve animal productivity and reduce urinary loss of N.