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EFFECTS OF GRASS MATURITY AND LEGUME SUBSTITUTION ON LARGE PARTICLE SIZE REDUCTION AND SMALL PARTICLE FLOW FROM THE RUMEN OF CATTLE’ J.G.P. Bowman2, C. W. Hunt3, M. S. Kerlef and J. A. Paterson4 University of Missouri, Columbia 65211 and University of Idaho, Moscow 83843 ABSTRACT Five ruminally and abomasally cannulated heifers (average weight 365 kg) were fed 6 kg/d of early (EOG) or late (LOG) maturity orchardgrass (OG) hay with or without replacement of EOG or LOG by 1.5 kg/d red clover hay (RC) in a 5 x 5 Latin square design. A fifth treatment, of LOG supplemented with 100 g/d casein (LOG+C), was used to evaluate the effect of supplemental protein. In situ fiber digestion, in vivo nutrient digestion and rate of passage from the rumen large (retained on a 1.68-mm screen; labeled with La) and small (passed a 1.68-mm screen; labeled with Sm) EOG and LOG particles were determined in heifers fed these diets. Early maturity OG hay had 20% and 62%, respectively, greater (P < .05) rates, and 61% and 73%, respectively, greater (P e .05) extents of in situ NDF and ADF disappearance than LOG. Red clover substitution for increased e .05) in situ extent of NDF disappearance by 6%. Early maturity large and small particles had 40% and 36%, respectively, greater (P e .05) rates of passage than LOG. Large and small particle ruminal pool sizes were increased (P e .05) by 115% and 33%, respectively, with Red clover substitution for increased e .lo) large and small particle output (kg/d) from the rumen by 15% and large particle rate of passage by 20%. Grass maturity may be affecting intake through rate of large particle size reduction and passage and particle passage, although legume supplementation of may influence intake by increasing rate of large particle size reduction and passage. Key Words: Maturity Stage, Particle Size, Flow, Beef Cattle, Dactylis glomerutum, Trifolium pratense J. Anim. Sci. 1991. 69:369-378 Introduction Clearance of digesta from the men is the primary process that affects forage intake by ruminants (Ulyatt et al., 1986). This process depends largely on digestion by ruminal microorganisms and on rate and extent of lJod Paper No. 11.169 of the Missouri Agric. Exp. +resent address: mpt. of ~nim. ~ci., ohio state bpt. of Sci., univ. IMO. %t. Sci., ~issouri. Received December 26, 1989. Accepted July 9, 1990. Sta. Univ., Columbus 43210 particle size reduction (Moseley, 1982). Forage particles must be reduced to a critical size before they can exit the men (Troelsen and Campbell, 1968; Poppi et al., 1980). Rate of particle size reduction is considered to be the main factor limiting digesta clearance from the men (Balch and Campling, 1962; Welch, 1982; Ulyatt 1986). Increased intake and rates of passage are observed when low-quality forages chopped or pelleted prior to feeding (Campling and Freer, 1966; Martz and Belyea, 1986. However, small particles (4.18 mm) have been shown to make up 72% of the DM in the rumen (Poppi 1981), and ruminal clearance may be limited by rate small particle removal 369
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This note was uploaded on 09/19/2011 for the course ANS 5446 taught by Professor Brown during the Spring '08 term at University of Florida.

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