Scientists see value of sugar grass to farmers

AgResearch finds link between high sugar grass and more vigorous grazing.

Higher sugar content in ryegrass cultivars is related to less fibre and protein and would likely encourage more grazing, according to research by AgResearch and Massey University.

Environmental benefits were also discussed in the research paper, one of four that focused on high sugar grass at the recent NZ Grassland Association conference at Waitangi, where almost 40 papers were presented to 300 scientists, industry representatives and farmers.

Germinal Seeds NZ Ltd, the wholesaler of Aber high sugar grass cultivars and a sponsor of the conference, said the science results confirmed farmers' reports of more vigorous grazing and increased milk and liveweight yields.

"It's reassuring to farmers when the science backs up their experience on-farm," said Germinal Seeds NZ Ltd general manager David Kerr.

The high sugar ryegrass composition project, funded by DairyNZ, analysed ryegrass pasture samples of the high sugar perennial AberDart, the standard perennial Impact and the short-term tetraploid Moata.

Samples for analysis were collected 8am and 4pm two or three times a week over four years (2004-2008) at Massey University's No. 4 dairy farm at Palmerston North.

A significant finding was a decrease in protein and fibre for every unit increase in WSC (water soluble carbohydrate, or sugar) and that the relationship remained consistent through spring and autumn.

The paper concluded that "an increase in WSC and a decrease in protein and fibre are both likely to have a positive effect on nutritive value and animal performance in most situations".

AgResearch scientist Dr Gerald Cosgrove presented the paper that referred to an environmental benefit in having a higher ratio of sugar to protein to enable more efficient utilisation of nutrient in the grazing animal.

"Provided the relationships demonstrated here hold true with further efforts to increase WSC through management or (plant) breeding, nutritional and environmental benefits should continue to accrue from greater WSC and from the associated reductions in protein and fibre."

Ryegrass having less fibre and the same concentration of WSC "could promote higher drymatter intake, which alone would be expected to increase production".

Research previously presented by Dr Cosgrove showed that cows grazing the high sugar ryegrass AberDart produced significantly more milksolids in autumn than cows grazing a standard ryegrass.

The soluble carbohydrate content of 18 different ryegrass cultivars regularly harvested in plots at Canterbury and Manawatu were listed in a paper from AgResearch scientists and PGG Wrightson Seeds.

Consistently higher concentrations of fructan, a significant component of WSC that's expected to deliver more metabolisable energy to grazing stock, were found in those cultivars selected for enhanced fructan.

Ten commercial cultivars and eight experimental lines of ryegrass were sampled and included annuals, perennials and the 'high sugar' types, of which the perennial high sugar grass AberMagic had the highest concentration of fructan at both sites over the 20 months.

A paper from AgResearch and University of Guelph (Canada) scientists described how to "harness the benefits of high sugar grasses through growth management".

Longer periods for regrowth in controlled environment growth chambers were found to increase the sugar content in grass and "notably in warmer environments".

"Overall the UK cultivar AberDart and a breeding line PG113 (experimental grass) maintained significantly higher levels of WSC in blades than UK and New Zealand control cultivars".

This was evident for both 10 degree and 20 degree days with night temperatures at 10 degrees Celsius, although WSC levels and recovery after defoliation had differed.

A paper from AgResearch and Lincoln University scientists showed the drymatter production of a high sugar grass and standard ryegrass were not significantly affected by different endophytes (fungi) introduced for pest protection when growing in irrigated conditions and under low levels of insect pressure.