The science behind Aber High Sugar Grasses
Cattle and sheep are inefficient at converting grass protein into milk and meat. When grazing conventional grass, livestock use only about 20% of protein from the herbage for production – most of the rest is wasted in urine. This is not only a waste of money, but it is detrimental to the environment.
A major reason for these losses is the imbalance between readily available energy and protein within the grass.
Proteins are rapidly broken down when feed enters the rumen but, when the diet lacks readily available energy, rumen microbes are able to use less of the nitrogen released from the feed. This results in a large proportion of the nitrogen being absorbed as ammonia and eventually excreted. Grass cell walls consist of complex carbohydrates called cellulose, hemicellulose and lignin.
Although these components can be broken down to provide energy, this is a relatively slow process and is often out of balance with the breakdown of protein.
Water soluble carbohydrates in grass are the sugars found inside the plant cells, rather than in the cell walls themselves. Unlike the carbohydrate in the cells walls, these sugars are a source of readily available energy soon after forage enters the rumen, fuelling the rumen microbes to process more of the grass protein. This protein can then be used in the production of milk and meat, rather than being excreted.
This is why livestock perform better off forage with higher sugar levels. Research at IBERS Aberystwyth University has shown that Aber HSG varieties have consistently higher levels of sugars than standard varieties, throughout any grass growing season. WSC levels up to 50% higher than controls have been recorded in some Aber HSG varieties. Results from trials are summarised later in this section.
The development of Aber High Sugar Grasses
Extensive research over 30 years has shown how high water soluble carbohydrate content in Aber High Sugar Grass varieties improves performance and profitability in milk, beef and lamb production.
Early research included:
- Grazing trials on commercial dairy and beef farms over two seasons
- Sheep studies at two research farms over three grazing seasons
More recent research with improved varieties that combine the high WSC trait with good disease resistance and high yields includes:
- Zero grazing studies to investigate the potential benefits of feeding Aber HSG to dairy and beef cattle on productivity and environmental impact
- Studies to investigate the digestive mechanisms that allow ruminants to utilise Aber HSG varieties more efficiently than other recommended grass varieties
- Field-scale grazing studies to investigate animal performance on Aber HSG swards
- Studies on the reduction of methane emissions from ruminants grazing Aber HSG ryegrasses.
Since proof of principle research established the value of a higher WSC content, a breeding programme has been ongoing to develop Aber HSG ryegrasses.
Following the first Recommended Grass and Clover List variety AberDart HSG in 2000, new varieties have continued onto the RGCL, with higher and higher levels of WSC and – as a result – continually improved performance potential.
Ongoing Aber HSG research
Research to improve the quality of grass continues at IBERS Aberystwyth University, with a focus on animal performance and increasing emphasis on the environmental benefits.
In addition to WSC, other quality traits including improvement of the fibre and lipid components of grass, are now included in project objectives.
Enabling ruminants to convert more of the nitrogen in their feed into milk and meat improves production efficiency. It is also very positive for the environment in terms of reducing greenhouse gas emissions (ammonia and nitrous oxide) and urea (in urine). Feeding ryegrasses with higher WSC content leads to improved rumen efficiency (allowing increased protein synthesis) and evidence shows this results in reduced nitrogen losses.
Aber High Sugar Grass varieties are proven performers in terms of dry matter yield, D-value and ME yield, boosting not only production from forage but the environmental credentials for farming too. This has been recognised with a string of prestigious awards, beginning in 2003 when the first Aber High Sugar Grass, AberDart HSG, became the first grass to
win the NIAB Variety Cup. In subsequent years, the plant breeders behind this breakthrough technology have collected innovation and technology awards from RASE and the BGS, and with the Queen’s Anniversary Prize and the recent Times Higher Education Award they have received accolades beyond the agricultural industry. In 2015, AberGreen became only the second grass to win the NIAB Variety Cup.
Aber High Sugar Grass for milk production
Results of several studies conducted on commercial dairy farms and by IBERS at its dairy unit near Aberystwyth show that grass protein is used more efficiently for milk production when extra energy is provided by feeding Aber HSG varieties.
Animals were fed either an experimental Aber HSG or a recommended control ryegrass variety. Both grazing and zero grazing techniques were used in the assessments.
The main advantages of feeding Aber HSG varieties were found to be:
- Milk yield increased substantially
In an early study that looked at Italian ryegrass across six commercial dairy farms, animals averaged 6% more milk per cow over the grazing season. In recent zero grazing trials with perennial ryegrass, the average milk yield of animals fed Aber HSG increased by 2.3kg/day in early lactation and by 2.7kg/day in late lactation, without a detrimental effect on milk quality.
- Dry matter intakes improved significantly
Zero grazing trials at IBERS completed in 2000 found that dry matter intakes rose by around 2kg/head per day. This is particularly important in low input farming systems where producers want animals to obtain as much of their nutrients as possible from grazed grass.
- Diet digestibility increased
In the same trial, a 3% improvement in diet digestibility was recorded with Aber HSG. The dry matter digestibility of the Aber HSG variety was found to be consistently higher than the recommended control variety
throughout spring, summer and autumn.
- The amount of feed nitrogen lost in urine is significantly reduced
In three zero grazing trials involving early, mid and late lactation animals, the amount of feed nitrogen lost in the urine was reduced by up to 24% from animals fed the Aber HSG variety. This has important implications for the environment in terms of nitrogen pollution.
Aber High Sugar Grass for beef production
Grazing trials and a companion zero grazing study run by IBERS at Aberystwyth have shown that when extra energy is provided to beef cattle by feeding Aber HSG varieties, grass protein is used more efficiently and animal performance is enhanced.
Research involved beef steers offered either an Aber HSG variety or a recommended control ryegrass variety. No extra additional feed was given, and grass intakes and liveweight gains were monitored regularly.
- Dry matter intakes of animals fed Aber HSG increased by around 25%, compared with those fed the control variety
- Greater intake was achieved because the Aber HSG variety was highly palatable. Additionally, Aber HSG was utilised more efficiently by rumen microbes and passed more quickly through the rumen
- Animals grazing Aber HSG recorded average daily liveweight gains of 0.997kg/head per day, which was 20% higher than the gain of cattle fed the recommended control variety
Performance of Charolais cross steers in grazing trials at Aberystwyth, Summer 2000
- In a separate zero grazing trial, animals fed an Aber HSG variety recorded high levels of growth performance, with an average liveweight gain of 1.3kg/head/day
- This bonus from Aber HSG was the result of higher forage intakes and greater efficiency of grass utilisation
- The growth rates of Aber HSG fed animals were enhanced, so they reached slaughter weights more quickly than those fed the control variety.
Aber High Sugar Grass for lamb production
In both upland and lowland situations, IBERS’ grazing trials have shown Aber HSG varieties to be superior in terms of animal performance, when compared with standard ryegrass swards.
- Initial studies on upland and lowland IBERS research farms showed that an early experimental Aber HSG variety supported significantly higher lamb growth rates
- In recent trials with Welsh Halfbred ewes and lambs, the liveweight gain of lambs was 20% higher where animals were grazing the Aber HSG variety
- In the same study, the carrying capacity (stocking rate) of the Aber HSG sward was 20% higher than the standard ryegrass sward
- Ad lib forage intake of grazing lambs was higher on the Aber HSG sward.