13 March 1998

Turning pipe-dreams into

reality

Plant scientists are using

traditional breeding

techniques alongside marker

assisted selection – and in

the long-term may use

genetic engineering – to

enhance forage quality.

Sue Rider reports

STRESS-resistant, drought-tolerant ryegrasses which are also winter hardy? Or how about non-bloating legumes, or grasses which supply more protein or energy to better meet the needs of the ruminant?

Pipe-dream or reality? The latter, hopes Chris Pollock, provided research at the Institute of Grassland and Environmental Research, Aberystwyth, where he is a director, reaches commercial fruition.

Plant breeders at IGER believe they can improve the quality of forages to better meet the needs of grazing ruminants. Increasing demands for home-grown protein sources would be met, too.

In the short-term forage quality will be improved using conventional breeding techniques aided by marker assisted selection – and in the long-term biotechnology could bring further benefits.

The BSE crisis has increased demand for sources of plant protein, such as soya, which are becoming expensive. There is, therefore, a considerable cost benefit as well as an environmental benefit in ensuring that ruminants make the best possible use of forage protein, explains Prof Pollock.

"IGER research should allow us to feed as much natural plant protein back to ruminants as we can. We are keen to promote maximum use of plant proteins in ruminant diets, and in turn to improve traceability and confidence in the food chain.

Improving the efficiency with which ruminants can use grass proteins, for example, would be a major benefit to livestock producers and is possible using conventional grass breeding techniques.

"We use a range of approaches to maximise the contribution that grasses can make to ruminant diets. At present our work is based on techniques which have been used at Aberystwyth since 1919 but we can now apply them with much greater precision because we have a clearer idea of what characteristics we should be looking for."

Animal nutrition research is enabling breeders to gain a better understanding of the traits needed to improve the efficiency of production and quality of ruminant products.

At present up to 40% of the protein in fresh grass is wasted because the rumen microbes fail to capture all the nitrogen released when plant proteins are broken down, explains Prof Pollock.

As soon as grass is eaten, its protein is rapidly degraded in the rumen of the animal and unless sources of readily fermentable energy are available, very little of the forage protein is converted into microbial protein – the major source of protein to the animal for growth and lactation.

This means that the balance between readily fermentable energy – carbohydrate – and rumen degradable protein is important.

"When the supply of protein and energy in the rumen is unbalanced or not available at the same time – in synchrony – large quantities of ammonia may be absorbed by the animal and excreted as urine before conversion into microbial protein, and later animal protein, takes place.

Improvements in the use of forage protein, and hence animal performance, can be made by increasing levels of readily fermentable energy, such as water soluble carbohydrates, in grass.

IGER grass breeders have been developing high WSC grasses using conventional techniques over the last 15 years.

As well as increasing the energy in grasses, researchers are studying the effect of stay-green characteristics on animal production.

In stay-green plants chlorophyll is broken down very slowly; leaf protein is, as a result, more stable and more is made available to the animal.

And just as breeders can produce grasses higher in energy and available protein without use of genetic engineering, they can also identify genes controlling useful plant characteristics and transfer them between species.

These techniques can, for example, improve the drought and stress tolerance of forages.

While tall fescue plants have poor feeding value, they are very stress tolerant, and are generally more disease resistant than ryegrasses. On-going breeding programmes at IGER are introducing beneficial traits from fescue into ryegrasses.

Researchers do not need to use genetic engineering to transfer stress tolerance from fescues into ryegrasses because the species used are similar enough to exchange genes freely when crossed.

This allows breeders to make hybrids and so transfer any fescue genes into ryegrass. The ryegrass genome remains undisturbed – except where the fescue genes are inserted.

Gene mapping and chromosome painting techniques have allowed researchers to identify where genes controlling stress tolerance lie on the chromosome – and therefore whether new hybrids produced contain valuable stress tolerance genes.

To create gene maps they use easy-to-detect labels or markers that are linked to the target genes. The idea is to test for the marker: if it is present, then the gene of interest is also there.

"This means that researchers can select for characters on seedlings without growing them in the field for two to three years," explains Prof Pollock. "We can look at the markers when the plant is tiny to check how the cross has gone."

This should speed up breeding programmes and hopefully allow breeders to produce new varieties in seven to eight years compared with the 10 to 12 years it takes at present, he adds.

But, when species are dissimilar and key genes cannot be transferred using conventional breeding techniques, genetic engineering is needed to insert these specific genes into plants.

IGERbelieves it can improve quality of forage to better meet the needs of grazing ruminants. Increased demands for home-grown protein would be met, too

GMFORAGES

&#8226 Not for the forseeable future.

&#8226 Must assess extent of gene flow.

&#8226 Depends on consumer acceptance.