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Document Type

Thesis - University Access Only

Award Date


Degree Name

Master of Science (MS)


Animal Science

First Advisor

Robbi Pritchard


beef cattle, blood ammonia, in situ, non-protein nitrogen


The objectives of this experiment were to compare N fluxes of Optigen, a slowrelease NPN source, with urea; whether pelleting affects Optigen N release; and N source effects on ruminal fiber digestibility. Dietary crude protein treatments were soybean meal (SBM), ruminally dosed Optigen (OD), Optigen incorporated into a concentrate pellet (OP), or ruminally dosed urea (UD). Diets were 50% forage (oat hay; 5.5% CP, 66% NDF) and 50% pelleted concentrate feed. Dietary CP was higher for OD and UD diets than for SBM and OP (12.6 v 11.2%; P < 0.01). Diets were fed to ruminally fistulated steers (BW 387 ± 28.9 kg) in a 4x4 Latin square designed experiment. Concentreate was fed and pulse doses of NPN occurred at 0800. Chronic sampling of rumen fluid and blood was done to follow postprandial changes in urea and ammonia concentrations. Mean rumen ammonia-N (RAN) concentrations differed among diets (4.9a, 8.9a, 6.6a, and 24.8b mg/dl, respectively; P < 0.01). A diet by time interaction occurred because of 60 min post feeding RAN concentrations of 8.7a, 31.2a, 22.1a, and 127.0b mg/dl, respectively (P < 0.01). Differences in plasma urea-N (PUN) mean concentrations (9.8a, 9.6a, 9.6a, and 12.3b mg/dl, respectively) included effects of time and diet by time interactions (P ≤ 0.01). At 60 min after dosing, PAN concentrations were highest for UD (P < 0.05). Mean plasma ammonia-N (PAN) concentrations differed among diets (0.6a, 0.6a, 0.7b, and 0.9c mg/dl, respectively; P ≤ 0.05). At 4 h after dosing, the UD diet caused lower (P ≤ 0.01) VFA concentration than other diets. At 1 and 4 h after dosing, UD diet caused higher ruminal pH than all other diets (P ≤ 0.01). Optigen had a slower rate of N release than urea, and was not adversely affected by pelleting. Because of a 16 h lag time after dosing, diet caused minimal differences in fermentation.

Library of Congress Subject Headings

beef cattle -- Feeding and feeds
Urea as feed
Nitrogen in animal nutrition
Fiber in animal nutrition


Includes bibliographical references (pages 29-35)



Number of Pages



South Dakota State University


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