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Unformatted text preview: J. Dairy Sci. 86:184194 American Dairy Science Association, 2003. Effects of Corn Grain Conservation Method on Ruminal Digestion Kinetics for Lactating Dairy Cows at Two Dietary Starch Concentrations M. Oba 1 and M. S. Allen Department of Animal Science, Michigan State University, East Lansing 48824 ABSTRACT Effects of conservation method of corn grain and di- etary starch concentration on ruminal digestion kinet- ics were evaluated. Eight ruminally and duodenally cannulated Holstein cows (55 15.9 days in milk; mean SD) were used in a duplicated 4 4 Latin square design with a 2 2 factorial arrangement of treatments. Experimental diets contained either ground high mois- ture corn (HM) or dry ground corn (DG) at two dietary starch concentrations (32 vs. 21%). Mean particle size and dry-matter concentration of corn grain were 1863 m and 63.2%, and 885 m and 89.7%, for HM and DG, respectively. Starch digestibility in the rumen was greater for HM treatments compared with DG treat- ments, but starch digestibility in the total tract was not affected by conservation method of corn grain because of compensatory digestion in the intestines. The differ- ence in ruminal starch digestibility between HM and DG treatment was greater for high-starch diets (71.1 vs. 46.9%) compared with low-starch diets (58.5 vs. 45.9%). This interaction is attributed to a greater difference in first-order digestion rate of starch between HM and DG treatment in high-starch diets (28.2 vs. 14.6%/h) compared with low-starch diets (16.8 vs. 12.2%/h). This suggests that ruminal starch digestion is a second-order reaction limited by enzyme activities as well as sub- strate availability; ruminal contents of cows fed low- starch diets may have insufficient amylolytic activity for maximal starch digestion when readily fermentable starch is available. Rate of neutral detergent fiber di- gestion in the rumen was slower for high-starch diets and HM treatments compared with low-starch diets and DG treatments, respectively. Effects of corn grain conservation method on ruminal digestion kinetics are greatly altered by starch concentration of diets. ( Key words: conservation method of corn, starch di- gestibility, digestion kinetics) Received March 18, 2002. Accepted June 11, 2002. Corresponding author: M. S. Allen; e-mail: email@example.com. 1 Current address: Department of Animal and Avian Sciences, Uni- versity of Maryland. 184 Abbreviation key: DG = dry ground corn; EE = ether extract; HM = high moisture corn; PDNDF = poten- tially digestible NDF; TRDOM = true ruminally de- graded OM. INTRODUCTION Starch is an important source of fuels for lactating dairy cows and for microbial protein production in the rumen. Although starch is potentially completely di- gestible, starch digestion is affected by a variety of fac- tors, such as type of grain (Herrera-Saldana et al., 1990), processing method (Galyean et al., 1981; Callison et al., 2001), conservation method (Ying and Allen,et al....
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