Barley

Nutritional Characteristics:

Barley is a cereal with medium content of both energy and protein, and while it can be used in poultry feeds, most is used in swine diets. Young birds are less able to digest barley, although this may be a consequence of ft-glucan content, and so this effect may relate to variety and growing conditions. The protein content of barley is usually around 11 - 12%, although much higher levels to 14 - 16% are sometimes encountered. These high-protein varieties are often little changed in content of essential amino acids. The lysine content of barley, within the range of 10 - 14% CP, is described by the equation 0.13 +0.024 x %CP. The metabolizable energy level of barley is correlated with bulk density, and there is a strong negative correlation with fiber.

Barley contains moderate levels of trypsin inhibitor, whose mode of action relates to sequestering of arginine, although by far the major problem with barley is content of ft-glucan.

Most varieties of barley will contain 4 - 7% ft-glucan, although with dry growing conditions that involve rapid maturation and early harvest, the content can increase to 12 - 15%. As previously described for wheat, the main problem of these ft-glucans is the bird's inability to digest the structure, resulting in the formation of a more viscous digesta. This increased viscosity slows the rate of mixing with digestive enzymes and also adversely affects the transport of digested nutrients to the absorptive mucosal surface. The rate of diffusion to the intestinal microvilli is a function of the thickness of the unstirred boundary layer, and this increases with increased digesta viscosity. Motility of the digesta will also indirectly affect the thickness of the unstirred boundary layer, which will also affect rate of absorption of all nutrients. The adverse effect of ft-glucan is most pronounced with nutrients such as fats and fat-soluble compounds. Adding synthetic ft-glucanase enzymes to diets containing more than 15 - 20% barley seems to resolve many of these problems, the usual outward sign of which is wet litter. Unfortunately, the description of exogenous enzymes is not standardized, as neither is the standard for units of efficacy, and so it is often difficult to compare products on the basis of the concentration of specific enzymes. Early studies show that any product should provide at least 120 units ft-glucanase/kg diet.

Enzymes seem to be less efficacious as the birds get older. Our studies show slight improvement in energy value of high ft-glucan barley when enzymes are used in diets for adult birds, and that some enzymes actually cause reduction in energy value when used with low ft-glucan barley. With this low ft-glucan barley, the addition of ft-glucanase enzymes actually caused birds to be in severe negative nitrogen balance for the 3 d duration of the balance study. For younger birds however, the efficacy of ft-glucanase enzymes is well established and many nutritionists consider barley plus enzymes as being equivalent in feeding value to wheat. These values can be used as a basis for economic evaluation of

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