Chemical and physical characteristics of grains related to variability in energy and amino acid availability in poultry

Grains such as wheat and barley, combined with legumes and oilseed meals, p rovide not only the bulk of essential nutrients for commercial poultry prod uction and reproduction, but are also the prime source of antinutritive com ponents, which are likely to have significant bearing on how effectively al l dietary components are utilised by poultry. Sources of variation in the p hysical and chemical characteristics of grains used in poultry diets includ e variety, seasonal effects, and growth sites, crop treatment and grain fum igants, and post-harvest storage conditions and period of storage. The avai lable energy and protein contents of grains fed to poultry, which best repr esent nutritive value, are extremely wide and in consequence there is an ur gent need to develop rapid and objective tests for the assessment of nutrit ive value prior to including grains in poultry diets. Variation in the avai lable energy and protein content of grains can be attributed to a wide rang e of anti-nutritive factors such as non-starch polysaccharides (NSP), enzym e activity, tannins, alkyl resorcinols, protease inhibitors, a-amylase inhi bitors, phytohaemagglutinins, alkaloids, saponins, and lathyrogens. The rel ative importance of such factors will also differ according to the type of grain in question. However, NSP seem to be the predominant factor in Austra lia over the past few years given the volume of published literature on thi s topic. This argument is strongly supported by the fact that NSP-degrading enzymes are routinely used in monogastric diets with great success through out the world. Numerous attempts over a long period have failed to provide unequivocal evidence that nutritive value in grains for poultry can be pred icted with sufficient accuracy and precision by simple, low-cost physico-ch emical measurements used singly or in combination. Nevertheless, it is high ly desirable to continue to explore these simple measurements in the expect ation that useful statistical relationships with more complex measurements will emerge, or that simple measurements can be used to fine-tune predictio n equations based on more powerful techniques such as near infrared spectro photometry. Finally, the nutritive value of grains for poultry will be determined not o nly by the chemical and physical properties of grains but also by the way t hat these interact with the processes of ingestion, digestion, absorption, and metabolism in birds. For this reason it is imperative that plant and an imal scientists join forces to improve the nutritive value of plant materia l as feed for animals for the benefit of grain growers and producers of liv estock.