By Robert Davies
AFTER TWO decades of plant breeding, Institute of Grassland and Environmental Research scientists reckon there is tremendous scope for further improvements in the naturally poor conversion of grass protein into milk and meat.
Mike Theodorou, head of IGER”s plant, animal and microbial biology department says protein use is poor because there is not enough available carbohydrate in most grass varieties for the rumen bugs to use to digest protein.
Instead, they use the amino acids released by plant protein breakdown as a source of energy. This process supplies no protein to the animal and excess nitrogen in the grass protein is excreted as ammonia.
Breeding varieties with higher levels of readily accessible water soluble carbohydrates in their cells creates a much more favourable nitrogen/sugar balance in the rumen, bringing both financial and environmental benefits.
Trials using IGER”s high sugar ryegrass AberDart show it can improve dry matter intakes by 2kg a head a day, increase grazing season milk yield by 6% and cut nitrogen lost in urine by 24%. Daily liveweight gains in beef cattle increased by 20%.
“We are seeing improvements in the recovery of available nitrogen and better conversion of plant to animal – milk and meat – nitrogen,” says Prof Theodorou. “This leads to improved livestock production efficiency. It may also help to reduce the loss of nitrate into drainage water and the escape of nitrogenous gasses into the atmosphere.”
Pete Wilkins, IGER”s manager of grass breeding, says high sugar varieties improve animal performance and make more effective use of applied nitrogen. “They have also kept pace with dry matter yield, persistency, cold tolerance and disease resistance objectives,” he says.
Dr Wilkins” team of grass breeders has access to a large amount of genetic material and more is being collected. The development of gene markers has given them more selection flexibility when trying to produce new varieties that meet producers” requirements.
But improvements in nutritional quality seen so far are just the beginning. Now Prof Theodorou”s team is looking at the way plant cells die. This can have a big impact on how efficiently fresh grass protein is used in the rumen and on pollutants reaching drainage water and the atmosphere.
Controlling the speed at which proteases – enzymes present naturally in grass – break down protein is the new challenge for grass breeders. It would delay the release of amino acids until the more complex carbohydrates in cell walls break down and provide the energy required by rumen microbes.