Forschungs- & Entwicklungsinformationsdienst der Gemeinschaft - CORDIS

Improved efficiency of use of grass protein and reduced environmental-N pollution by ruminants consuming grass of high WSC content (< 20-25% WSC/g DM)

The overall objective of the SweetGrass project was to provide sound scientific evidence for the advantages (production and environment) of using novel ryegrasses bred for their high water soluble carbohydrate content (using conventional plant breeding programmes) in grassland-based, sustainable ruminant production systems. Previous proof of principle work funded nationally in the UK demonstrated significant production responses and beneficial alteration in N-partitioning (improved nitrogen use efficiency; NUE) in zero-grazed dairy and beef cattle and in grazing lambs offered an experimental ryegrass bred to express relatively high concentrations of water soluble carbohydrate (WSC).

The SweetGrass project examined this phenomenon in more detail using a commercially available (AberDart: NIAB-certificated) high-WSC forage and more realistic grazing and conservation settings. The results can be summarised under three main areas as follows:

- Ability of grasses high in WSC to alter N-utilisation efficiency and reduce N-pollution from faeces and urine.
- Ability to conserve WSC in silage made from grass high in WSC.
- Ability of AberDart (bred to express high levels of WSC) to accumulate WSC in agronomy plots and in large field trials.

Each areas corresponds to an exploitable result and this section provides a summary of the work behind the exploitation of area 1 (areas 2 and 3 are covered in analogous parts of the e-tip).

A major objective within the SweetGrass project was to highlight the potential benefits to rumen function and N use efficiency accruing from the use of grass varieties bred for high WSC content. Two approaches were used to test the efficacy of grasses and silages with elevated WSC content in rumen function and livestock production experiments. One approach used in vitro experiments to examine the influence of WSC in feed on the efficiency of rumen microbial protein synthesis. In the second approach, in vivo experimentation undertook digestion studies with beef and dairy cattle to examine the effects of high WSC in grazed and ensiled forage on rumen function and/or meat and milk production. Dairy cow experiments also investigated the effects of feeding mixtures of elevated WSC grass silage with and without red clover silage. In addition to production measurements, the research also considered the potential impact of feeding grasses with elevated WSC content on reducing environmental-N pollution.

From the in vitro and in vivo studies two conclusions can be drawn. Firstly, some experiments demonstrated that it was possible to improve N-use efficiency in the rumen. Secondly, under certain conditions, the efficiency of conversion of plant to animal N could be improved, reducing the amount of N excreted to land in faeces and urine. While improvements in efficiency were sometimes observed in animals receiving low/no concentrate feeds, when high levels of energy and protein in concentrates were fed, they appeared to mask or negate the beneficial effect of feeding the high WSC forage.

A difficulty encountered in this part of the project was that the grasses bred for high WSC content often failed to display the trait when cultivated in farmer fields (as opposed to agronomy plots), making the high WSC grass indistinguishable from the control varieties. Thus in comparisons involving grass bred for high WSC, while production responses were generally high, it was often not possible to conclude a discernable benefit over and above that of the control variety. Nevertheless, when considered in terms of proof of principle, results were sufficiently robust to conclude that, under the appropriate conditions, high WSC concentration in both grazed and ensiled forage, if achievable, can lead to an increase in the efficiency of production response and reduced environmental N-pollution, particularly in ruminants reared in more extensive grassland production systems.

Verwandte Informationen

Reported by

Institute of Biological, Environmental and Rural Sciences
United Kingdom
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