CHOOSING GRAIN OK FOR GAIN
IT IS often said that growers run around like headless chickens, trying to keep up with market demands. Now, the poultry industry itself is having an increasing impact.
No one can blame it for wanting the best value from its feed constituents, however. It uses about 2m tonnes of the UK wheat crop to feed about 300m chickens a year, so it has reason to be demanding.
Until recently, wheat grain was selected on a least cost basis, since all varieties were considered equally nutritious. But HGCA-funded work coupled with in-house research by feed companies has shown that there are significant differences in the dietary energy of different wheats.
Initial studies focused on environmental influences on the feeding value of wheat. Like with baking quality, feed quality depends to some extent upon crop growing conditions and inputs. For example, high levels of nitrogen fertiliser increase protein and amino acid content and digestibility.
Based on this work, current advice is to apply optimum nitrogen rates for maximum yield. Higher levels may improve protein quality but they wont increase apparent metabolisable energy (AME), explains HGCA project leader and reader in animal production at the University of Nottingham, Dr Julian Wiseman.
"AME is the standard measure of dietary energy in poultry. It would seem to be influenced by environmental factors, but by far the most significant is the variety of wheat used. That has become the focus of current research."
With collaboration from the John Innes Centre, Nickerson UK and BOCM Pauls, Dr Wiseman is using near-isogenic breeding lines to check the nutritional consequences of each genetic character. That way he hopes to pinpoint varieties which offer the qualities looked for by the feed compounders.
"A near-isogenic line is a sample of wheat which is identical to another except for one character. So rather than compare named varieties which have a medley of characters, we can examine the benefits of each individual feature. Then we can pick out the varieties which exhibit the desirable characteristic," he explains.
A typical poultry diet consists of about 65% wheat, with varying quantities of soyabean, fishmeal, vegetable oil, vitamins and minerals. With its high starch and protein content, wheat supplies much of the energy needed by the birds.
Getting the best possible level of energy coupled with the most efficient digestibility of starch and protein is the aim of the feed manufacturer. The premium feeds sell for a higher price because they allow chickens to grow faster and produce less waste.
He and his colleagues are currently looking at about 10 characteristics to see which are most desirable. So far, some of them have proved negative to digestibility, so in theory the best varieties are those which dont possess those characteristics.
Luckily for collaborator Nickerson UK, it just so happens that one of its current varieties is more appropriate than other types for poultry feed. Buster is a hard endosperm wheat with no wheat/rye translocation in its genetic makeup.
Bill Angus, senior wheat breeder for Nickerson UK, explains the significance of this. "Using near-isogenic lines, we have shown that hard endosperm wheats are more easily digested in chickens. Hard wheats allow the digestive juices to break down starch more efficiently, so reducing the amount of waste."
Rye contains proteins called secalins, which make the wheat flour stickier. This is undesirable for bread wheats and for biscuit wheats, and is now known to be detrimental in poultry rations.
Mr Angus explains why. "Wheat which produces a sticky dough has a similar effect in the chickens gut. Viscous gut contents prevent the efficient absorption of nutrients, which slows down the birds growth rate and produces the sticky dropping syndrome, so the carcasses may be downgraded."
Ideally, poultry feed should contain wheat without the rye gene. However there are few UK feed wheat varieties grown in large amounts without it – the exceptions are Buster, Reaper, Consort, Riband and Claire. Of those, Buster and Reaper are the only ones with a hard endosperm.
"Most of the feed wheats introduced in the past 10 years or so have the rye gene, because breeders perceive it gives the variety a slightly more consistent or higher yield. But this work may change the direction of breeding in future, and see the rye gene disappear."
THE animal feed industry has long been the recipient of wheat rejected for bread and biscuit making. It was thought that poultry and pigs could receive much needed dietary energy, crude protein and amino acids from any type of wheat grain.
But new research highlighting the differences in nutritional value of wheat varieties has made the feed industry more concerned about what it buys. As the largest single user of wheat, it feels justified in specifying exactly what is required to meet its needs.
The main criteria is that wheat, which commonly amounts to 65% of the diet, should be of a high energy value and easily digested. Early work by the University of Nottingham using named varieties found substantial differences in digestibility between individual samples, but couldnt find any conclusive evidence for consistent differences between varieties.
However further studies on near-isogenic lines – varieties identical except for one single genetic character – proved more fruitful.
While the growing conditions to which wheat is subjected can also have an effect upon dietary energy levels and digestibility, it is now thought that certain characteristics within varieties are the best criteria for selecting the best non-ruminant feed wheat.
Some feed compounders now specify particular varieties, and either offer guaranteed contracts of sale or premiums for those. It may not be long before the feed industry, like the milling industry, has a major influence on which varieties are grown.