Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Animal Science

First Advisor

James R. Russell


Samples of corn leaves, cornstalks, and alkaline hydrogen peroxide(AHP)-treated cornstalks were incubated in situ for 0 to 48 h in the rumen of a fistulated cow fed alfalfa hay. Cellulase from microorganisms attached to undigested residues was extracted and assayed using either trinitrophenol-cellulose (TNP-C) or carboxymethylcellulose (CMC) as substrates. Enzymatic hydrolysis of TNP-C was linear with enzyme concentration and time and did not release free TNP. Correlations between the amount of neutral detergent fiber (NDF) digested per h and the specific activity of cellulase from ruminal microorganisms attached to corn leaves, cornstalks and AHP-treated cornstalks at each incubation time were.90,.63;.70,.95; and.30,.70 for the TNP-C and CMC substrates. Five rumen cannulated steers were fed diets composed of 80% ground cornstalks and 20% (DM basis) supplements containing low urea and high phosphorus concentrations (7.2% CP; 0 g urea fermentation potential (UFP) kg[superscript]-1DM;.26% P in the total diet), high urea and high phosphorus concentrations (8.6% CP; -5 g UFP kg[superscript]-1DM;.26% P), low urea and low phosphorus concentrations (7.2% CP; 0 g UFP kg[superscript]-1DM;.18% P), broiler litter ensiled at ambient temperature (8.5% CP; -1.1 g UFP kg[superscript]-1DM;.26% P) or broiler litter ensiled at 45°C (8.5% CP; 0 g UFP kg[superscript]-1 DM;.26% P) in a Latin Square design. The proportions of protein that were slowly degraded (P <.05) and estimated to escape ruminal degradation (P <.10) were greater in broiler litter ensiled at 45°C than in that ensiled at ambient temperature. Organic matter (OM) intake, the liquid turnover rate, and the mean proportion of microbial-nitrogen and specific activity of cellulase (measured with CMC) bound to rumen particles were lower (P <.05) for steers fed cornstalks and the low urea-low phosphorus supplement than steers fed other diets. Digestibilities of OM and NDF, NDF digestion kinetics, and the rate of passage of ruminal solids were not affected by supplement composition. Nitrogen retention was greater (P <.05) in steers fed cornstalks supplemented with broiler litter ensiled at 45°C than in steers fed diets containing the other supplements. Measurement of cellulase activity of microorganisms attached to rumen particles with either TNP-C or CMC substrates provided a sensitive method to monitor changes in the microbial population caused by alterations in the physiochemical structure of a forage or the nutritional composition of the diet of ruminant animals.



Digital Repository @ Iowa State University,

Copyright Owner

Tito Efrain Diaz-Munoz



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140 pages