Degree of Starch Access (DSA): Starch Digestibility in Forages and Grains fed to Dairy Cattle
نویسنده
چکیده
Starch, supplied in Midwest diets primarily from high-moisture and dry corn grain and whole-plant corn silage, is an important source of energy for dairy cattle. However, the digestibility of corn starch can be highly variable. Various factors, particle size (fine vs. coarse grind), grain processing (steam flaked vs. dry rolled), storage method (dry vs. high-moisture corn), moisture content of high-moisture corn, type of corn endosperm, and corn silage maturity at harvest, chop length, and kernel processing, influence ruminal and or starch digestibility in lactating dairy cows. Because both physical and chemical properties of starch influence starch digestion, assessment of starch digestibility in the laboratory has been challenging. In an attempt to address variation in starch digestibility, NRC (2001) suggested empirical processing adjustment factors (PAF) to adjust non-fiber carbohydrate digestion coefficients for high-starch feeds. However, since no system to measure variation in processing adjustment factors for feedstuffs is available the PAF’s are subjective book values with minimal practical application. For corn silage, Ferreira (2002) developed a kernel processing score (KPS) to assess adequacy of kernel processing of corn silage. But, KPS only considers particle size and does not consider the influence of moisture content and endosperm type on starch digestion. Some commercial laboratories employ in situ or in vitro systems to evaluate starch digestibility, but methods are variable between laboratories and to date relationships to in vivo starch digestion are not well defined.
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