Document Type

Thesis - University Access Only

Award Date


Degree Name

Doctor of Philosophy (PhD)

Department / School

Animal Science


Three crossbred steers (BW = 368 kg) fitted with simple cannulae into the rumen and t-type cannulae into the proximal duodenum were used in a 3 x 3 Latin square design to determine the effect of level and source of crude protein (CP) on flow and digestibility of nutrients and the effect of particulate phase marker choice (chromic oxide versus ytterbium) on estimation of these variables. Steers were fed 92% concentrate, whole shelled com-based diets that were either 10% CP from urea or 12.5% CP from either urea or soybean meal. Estimates of ruminal digestibilities were similar for both markers, while greater post-ruminal digestibilities were estimated by chromic oxide. Increasing CP level from 10 to 12.5% with either urea or soybean meal resulted in increased bacterial crude protein (BCP) synthesis and more efficient production of BCP. There was no advantage to supplying supplemental CP from soybean meal compared to urea, however low OM intake (5.10 ± .27 kg/d) may have precluded a response. Given this underlying problem of in vivo studies, an in vitro batch culture procedure was developed to detect nutritional deficiencies which limit BCP synthesis. Two crossbred steers (BW = 600 kg) were fed a 92% concentrate, com-based diet deficient in degradable intake protein (DIP). Batch cultures were established using whole ruminal contents (100 g) at 3 h post-feeding in 250-mL polypropylene bottles fitted with rubber stoppers and one way gas valves. Treatments (Trial 1) were 1) Control (no added substrate), 2) Starch (5 g), and 3) NPN (urea at a level to raise ammonia N concentration by 5 mg/dl) incubated for 1, 2, 4, 6, or 12 h. Adding urea improved BCP production, thus detecting the DIP deficiency. Starch did not improve BCP synthesis compared to Control. Maximization of BCP production occurred at 2 h of incubation. In Trial 2, five replicates of seven treatments were established and incubated for 2 h. Treatments were Control, Starch, and five ratios (100:0, 75:25, 50:50, 25:75, and 0:100) of urea: Peptone on a N equivalent basis at the same level as in Trial l. Net BCP synthesis was negative for all treatments. Combinations of urea and Peptone numerically slowed the loss of BCP compared to Control. Lack of anaerobic conditions, a shift in exponential growth compared to Trial 1, and(or) possible effects of long term consumption of a DIP deficient diet are implicated and should receive future experimental consideration.

Library of Congress Subject Headings

Beef cattle -- Feeding and feeds

Proteins in animal nutrition

Proteins -- Synthesis



Number of Pages



South Dakota State University