Rezultaty
The overall objective of the project was to provide sound scientific evidence for the advantages (production and environment) of using novel ryegrasses bred for their high water soluble carbohydrate (WSC) 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 WSC. The SweetGrass project examined this phenomenon in more detail using commercially available (AberDart: NIAB-certificated) high-WSC forage and more realistic grazing and conservation settings.
The results can be summarised 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.
Each areas corresponds to an exploitable result and this section provides a summary of the work behind the exploitation of area 2 (area 1 is covered in analogous parts of the etip)
The concentration of WSC in forage for ensilage is important to ensure that the crop is acidified rapidly by lactic acid producing bacteria thereby conserving nutrients, reducing losses and providing effective preservation of the ensiled herbage on long-term (over-wintering) storage of the ensiled herbage. Lack of availability of WSC or an inappropriate epiphytic microbial population on the crop often results in the production of silages of poor nutritional and hygienic quality and reduced aerobic stability and this can have a profoundly negative effect on the productivity of silage-fed livestock. Enhancing the WSC in forage grasses through conventional plant breeding provides for the opportunity to improve silage quality, particularly where the conservation process is managed take maximal advantage of the additional WSC in the herbage.
Management strategies include (a)wilting procedures after harvest but prior to ensilage to ensure that WSC levels are concentrated in the herbage and(b) the application of appropriate acidifying chemical additives or homofermentative lactic acid bacteria to herbage during harvest to rapidly acidify (conserve) the crop. While both of these strategies can result in dramatic improvements silage quality, where WSC concentration in herbage are high enough to exceed that required for optimal conservation, it is conceivable that WSC can be conserved and made available subsequently, upon feed-out, as a rapidly fermentable energy source for the rumen microbial population.
A major objective within this project was to devise and demonstrate improved conservation strategies which take advantage of elevated levels of WSC in grass and grass-legume mixture. Improvements in silage quality were measured in terms of (a)nutritional quality, (b)hygienic status, (c)aerobic stability and (d)the ability to conserve WSC in silage for subsequent utilisation by the rumen microbial population.
From the research conducted the following conclusions were drawn:
- Fast efficient wilting with a minimum of losses in the field due to respiration or leaching was shown to be the most important pre-condition for successful ensiling of grasses with high WSC content.
- If, due to inclement weather, wilting was not an option, chemical additives, either acid based or combinations of ingredients active against clostridia, were the most effective treatments for improving high WSC, wetter silages. Where making silage when no additive is used (the case for most EU farmers) using a grass of elevated WSC will greatly enhance the probability of achieving good preservation. This is particularly evident with wetter forages (results confirm this).
- In silages of high DM content, biological inoculants usually contributed to lower fermentation losses and ammonia concentrations, although they also increased the tendency for aerobic spoilage in the resultant higher quality silages.
- Co-ensiling mixtures containing up to 50% legume (red clover or lucerne were studied) enhanced silage quality and aerobic stability and reduced fermentation losses.
In terms of the impact of these results on grassland-based, livestock agriculture, it is concluded that the farming community will derive considerable economic benefit by ensuring that high WSC grasses are used for re-seeding swards and by adopting some/all of the management strategies advocated above. In addition to financial reward, it is also considered that these improved conservation practises will lead to reduced waste and more hygienic conserved crops, thus having a positive impact on the environment, on animal welfare and on the quality of life of livestock producers and consumers.
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.
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