The Science behind HSG

Cattle and sheep are actually poor converters of grass protein into milk and meat. When grazing ordinary grass, livestock use only about 20% of protein from the herbage for production - most of the rest is wasted in faeces and urine. This is not only financially costly, but also 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. However, when the diet lacks readily available energy, the rumen microbes can use less of the nitrogen released from the feed, so much of it is absorbed as ammonia and eventually excreted.

Water soluble carbohydrates in grass are the sugars found inside the plant cells, rather than in the cell walls themselves. They become a source of readily available energy soon after forage enters the rumen, allowing rumen microbes to process more grass protein. This protein can then be used in the production of meat and milk.

Through this mechanism, HSG varieties, with high levels of water soluble carbohydrates, can significantly improve the utilization of protein in grass. Research at IGER and AgResearch has shown that HSG varieties have consistently higher levels of sugar than standard varieties throughout the grazing season. Water soluble carbohydrate levels up to 40% higher have been recorded in some HSGs. However, studies have shown even a small difference in the level of water soluble carbohydrates can have a big effect on ruminant performance.

Several trials involving dairy and beef cattle, as well as sheep, have demonstrated significant performance benefits from feeding HSG varieties.