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EFFECTS OF DIETARY FIBER AND FEEDING FREQUENCY ON RUMINAL FERMENTATION, DIGESTA WATER-HOLDING CAPACITY, AND FRACTIONAL TURNOVER OF CONTENTS’j2 Mark A. Froetschel and Henry E. Amos The University of Georgia3, Athens 30602 ABSTRACT To determine the effects of different sources of fiber and feeding frequency on digesta water-holding capacity (WHC g HzO/g DM) and ruminal liquid contents, four ruminally fistulated Jersey steers were fed a 60:40 roughage-concentrate diet at 1.5 times &. Diets contained either sorghum silage (SS) or a 67:33 mixture of SS and soyhulls (SH) as roughage and were fed either once or 12 times daily, in a 2 x 2 factorial experiment with 15d periods. Ruminal fluid was sampled at 2,4, 6, 8, 10, 12, 16,20, and 24 h after a dose of Co-EDTA on d 10 and analyzed for Co, VFA, ammonia, buffering capacity, and osmolality. Ruminal WHC, NDF, ADF, lignin, and starch were measured in samples obtained by ruminal evacuation at 3,6,12, and 24 h after feeding on d 11,12,14, 15, respectively. Substitution of SH for SS decreased ruminal pH .32 Units and dilution rate by 26.8% but increased total VFA by 10.9%. osmolality by 13.6%, and the fractional turnover rate (FIR) of ADF by 22.5% (P < .05). Frequent feeding resulted in 4.7, 21.9, 74.4% increases in total and FIR of ruminal DM and starch (P < .OS), respectively. Interactions (P < .05) were observed between dietary fiber source and feeding fiequency for ruminal fluid molar percentage acetate to propionate ratio (A/€’), liquid volume (evacuated), and WHC (kilograms). Substituting SH for SS decreased ruminal WHC (kilograms), liquid volume, and A/P only in steers fed once daily. Ruminal WHC (kilograms) was correlated positively with ruminal liquid volume but negatively with DM FIR. The dynamics of digesta WHC (kilograms) associated with dietary fiber source and feeding frequency suggest that it may influence the contribution of water and salivary secretions to liquid contents. Key Words: Steers, Rumen, Water Holding Capacity, Fiber, Feeding Frequency) J. Anim. Sci. 1991. 69:1312-1321 introduction Water-holding capacity (WHC), a physical property of fiber, has been related to human colonic digesta passage (McConnell et al., 1974; Stephen and Cummings, 1979; Robert- son and Eastwood, 1981). In ruminants, WHC lSupported by State Hatch funds allocated to the Georgia Agric. Exp. Sta. the Georgia Agricultural Commodity Commission for Milk. he auttms appreciate the technical assistance of Pelicia Kauk and Clara Parker. kept. Dairy Sci. Received June 15, 1990. Accepted October 3, 1990. may affect ruminal liquid pool size and the rate and extent of ruminal digestion (Mertens, 1977; Owens and Goetsch, 1986; Allen and Mertens, 1988). Digesta WHC may influence the extent to which salivary secretions are retained intraruminally and, thereby, influence the relationship between salivary production and liquid outflow (Froetschel et al., 1989a). The effect of WHC on gut function is related to the susceptibility of fiber to fer- mentation (McBurney et al., 1985). Therefore, the influence of WHC on the ruminal liquid environment may depend on the fractional turnover rate (FTR) of digesta; FIX represents the combination of both digestion and passage.
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