Wheat, Energy and Broiler Performance

Cereals provide much of the energy in poultry feeds, corn in the US and parts of Canada, wheat in Western Canada, parts of Europe, and Australia.  The cost of feed energy (apparent Metabolizable Energy, AME) is the single greatest cost of poultry production, and the amount of energy in a cereal is essential knowledge for adequate poultry nutrition.

Feed mills use a process called “least-cost formulation” to calculate which ingredients to use in a mixed feed and in what proportions.  This ensures that the requirements of the specific type of bird are met at the minimum cost.  To use least-cost formulation, nutritionists need values for the requirements of the bird, the cost of the available ingredients, and their nutrient contents.  Despite changes in production due to genetic selection, nutrient requirements are fairly well understood.  Ingredient costs can change rapidly, but their calculation is direct.  A weak link in the chain of least-cost formulation is the determination of the nutrient content of some ingredients, particularly in the energy content of cereals other than corn. 

The US National Research Council (NRC, 1994) provides the nutrient contents of many feed ingredients, including wheat, and these values are commonly used for feed formulation.   NRC provides two energy values for wheat: 2,900 kcal/kg for hard red winter wheat (3,330 kcal/kg on a dry matter basis), and 3,120 kcal/kg (3,510 kcal/kg on a dry matter basis) for soft white winter wheat.  What happens if these values are wrong?  If the values are too low, feed will be over-formulated and the extra energy will increase the cost of the feed.  If they are too high, feed will be under-formulated and performance may be compromised.  Either way, the producer has less control of the feeding program.

There has been a feeling in Western Canada that the values provided by NRC for the energy in wheat are too low.  It is known that both the genotype (cultivar) and the environment in which the wheat is grown affect the AME value.  The AME of wheat was investigated by Dr. Tom Scott at the Pacific Agri-Food Research Center (PARC) in Agassiz, in collaboration with H. L. Classen, M. L. Swift, and M. R. Bedford in a study funded by The Alberta Barley Commission, The Canadian Wheat Board, Finnfeeds International, IRAP/NSERC, The BC Broiler Chicken Marketing Board, and Agriculture and Agri-Food Canada.

Using a bioassay for broilers that was developed at PARC, Dr. Scott measured the energy derived from 108 samples of wheat of nine different varieties grown in three locations in Western Canada over a two-year period.  This bioassay measures not only the AME of the sample, but also the viscosity of the intestinal contents of birds fed the cereal (measured as centipoise), and their performance.  The intestinal viscosity is measured to determine the anti-nutritive effects of soluble non-starch polysaccharides (NSP), which wheat contains.  High levels of NSP produce a viscous solution in the gut that interferes with digestion, especially in young birds, and produces sticky droppings.  Enzymes can be added to the feed to counteract these effects, and because this practice has become widespread, it was done for one-half of each of the samples.

As expected, both the year and the specific growing environment affected the feeding value of the samples.  The growing environment is difficult to control, and knowing that there are differences simply points out that routine tests may be necessary.  Knowing the effect of the cultivar is more useful.  Table 1 shows the nine cultivars of wheat tested along with the class of wheat to which they belong.  Durum wheat is primarily used in the production of pasta, Canadian Prairie Spring (CPS) cultivars (Glenlea is actually considered a feed wheat) are used extensively in animal feed, and Hard Red Spring (HRS) wheat is traditionally valued the most because of the high protein content. 

Table 1 (below) also shows that both the digesta viscosity of the broilers and the AME obtained were dramatically different for these nine wheat cultivars.  With no enzyme supplementation, digesta viscosity was lowest for the Durum wheat varieties and highest for the HRS varieties.  Enzyme supplementation dramatically reduced the intestinal viscosity and the anti-nutritive properties of the NSP.  It also removed much of the difference between the cultivars.  Along with the differences in intestinal viscosity, there were marked differences in the AME extracted by the birds and without enzyme, there was about a 10% difference between the highest and lowest values.  The AME values for the Durum varieties were well above those given by NRC.  With enzyme supplementation, all nine cultivars had AME contents that were higher than either value provided by NRC. Even with enzyme supplementation, Durum cultivars still contained more than 100 kcal/kg more energy than other cultivars.

Table 1.  The digesta viscosity and AME for nine cultivars of wheat in diets with and without enzyme supplementation.

Digesta Viscosity (centipoise) AME (kcal/kg)

a-e Means within followed by no common letter are significantly different at P < 0.05.
1CPS is Canadian prairie spring wheat, DUR is durum wheat, and HRS is hard red spring wheat.

How does this relate to broiler performance?  Table 2 (below) confirms what was seen above in Table 1.  There were significant differences between cultivars, with the Durum wheat cultivars producing the heaviest broilers at 17 days, and doing it most efficiently.  Enzyme supplementation significantly improved performance and it reduced the difference between cultivars. 

Table 2. Performance of chicks fed nine cultivars of wheat in diets with and without enzyme supplementation.

17-day Body weight (g)          Feed:Gain Ratio (g:g) 

a-f Means within followed by no common letter are significantly different at P < 0.05.
1CPS is Canadian prairie spring wheat, DUR is durum wheat, and HRS is hard red spring wheat.

These data reflect several problems with current feed formulation when wheat is the major energy source.  The wheat cultivars differed considerably.  Durum wheat is likely undervalued for growing broilers, the CPS cultivars had lower energy values than other types, and the HRS cultivars produced the highest intestinal viscosity.  When wheat-based diets are supplemented with enzymes to reduce the effects of NSP, the AME values reported by NRC are too low.  This could result in over-formulation and increased feed costs. 

It seems clear from these data that when using least-cost formulation of broiler diets, feed mills should consider the cultivar of wheat being used and whether it will be supplemented with enzyme.

References:

National Research Council, 1994.  Nutrient Requirements of Poultry. 9th ed. 

National Academy Press, Washington, DC. Scott, T. A., F. G. Silversides, H. L. Classen, M. L. Swift and M. R. Bedford, 1998.

Effect of cultivar and environment on the feeding value of Western Canadian wheat and barley samples with and without enzyme supplementation.  Can. J. Anim. Sci., in press.

Dr. F. G. Silversides is a scientific writer living on Denman Island, British Columbia, Canada.