1 October 1999

Variety key to wheat feed value

By Emma Penny

LOW wheat prices mean compounders – and producers – are keen to use it in greater quantities in rations, and now researchers aim to find out whether stock perform better when fed specific varieties.

Angela Moss, researcher at ADASs Feed Evaluation and Nutritional Sciences unit at Stratford-upon-Avon, Warks, says this interest initiated research into the effect of variety on the nutritional value of wheat, funded by the Home Grown Cereals Authority.

"As the wheat price plummeted, compounders wanted to put more into rations. However, they were concerned about it fermenting rapidly, causing acidosis and other problems. This meant they had traditionally limited its proportion in feeds, increasing ration energy content by adding maize grain which is more slowly fermentable."

But with the temptation of much lower prices, compounders wanted to know whether all feed wheats were the same – did all varieties have rapidly fermented starch?

Initial work centred on samples from HGCA trials. These were tested in the lab to see whether variety, crop management, or other factors had an effect on nutrition, explains Dr Moss.

"We found quite a range in the extent and rate of fermentation between wheats, and felt this could have an impact on the amount that could be fed in rations.

"Grain nitrogen content had an effect; the higher the grain N, the slower the rate of fermentation."

Dr Moss says researchers believe slower fermentation is due to protein coating starch granules in the grain. This means rumen microbes have to work through the protein before they can get at starch, so slowing fermentation.

"Earlier HGCA-funded work on feeding wheat to poultry showed that grain endosperm type had an effect on ME, so we also considered this."

Wheat varieties with a steely endosperm – which looks translucent – were found to ferment more slowly. Varieties with a steely endosperm were mainly hard wheats such as Brigadier or Hereward, she says.

Varieties with a mealy endosperm – which looks white and almost floury – fermented more rapidly. These were predominantly soft wheats such as Riband and Consort.

"We found that high nitrogen hard wheats were least fermentable in the rumen, while low nitrogen soft wheats were fermented fastest," says Dr Moss.

But, she adds that it was evident that there was great variation in mealy and steely endosperms in some samples. "This is mainly an environmental factor, but will have an effect on how fermentable the wheat is. But it shows that its not just variety that has an effect – endosperm texture must also be considered."

The second phase of work – funded by the Milk Development Council – involved feeding selected wheats to cows at the unit to confirm lab results, which proved successful.

Now, Dr Moss is to start a commercial feeding trial on dairy cows at ADAS Bridgets, Hants. Cows in the study will be fed rations containing either slowly or rapidly fermented wheats to see what effect fermentation speed has on milk yield and composition. Different levels of wheat inclusion in rations will also be considered.

"We are in the process of collecting samples for this to ensure we get extremes in fermentation speed," she explains.

The trial will finish next spring, but Dr Moss says results so far should allow producers to make informed decisions about buying wheat for feeding – or sowing varieties for next years harvest.

"Choosing a variety for feeding depends on what you want to achieve and what else you are feeding with it."

On an all-grass farm, where dairy cows are likely to have access to high nitrogen grass silage with a reasonably high ammonia level, feeding a more rapidly available starch – a low nitrogen, soft wheat – should help capture more nitrogen in the rumen, says Dr Moss.

But high genetic merit herds producing high yields, feeding a maize and grass silage rations will probably want more bypass starch to maximise milk proteins and ensure more energy is directly available to the cow. "In this case, a slowly fermented starch – a high nitrogen, hard wheat – is the best option."

Once the feeding trial is completed, Dr Moss believes that NIAB should consider including a feed value for each variety in its lists. "Scores for milling and biscuit qualities are already included for each variety, but theres nothing on feed quality.

"We could develop our lab testing to look at samples from NIABs trial plots and score wheat varieties according to feed value for ruminants and poultry – and we could also do it for barley.

"Poultry producers already offer growers a premium to grow certain varieties, and that could carry over to farmers buying wheat to feed cattle, which would benefit arable producers too," she adds. &#42

VARIETY CHOICE

&#8226 Slow or rapid fermentation?

&#8226 Low or high grain nitrogen?

&#8226 Soft or hard wheat?

&#8226 Environment important.