Bibliographic record
Abstract
A series of experiments were conducted to investigate how dietary and ruminal factors regulate urea-N recycling in ruminants.In Experiments 1, 2, and 3, urea-N kinetics were measured using 4-d intra-jugular infusions of [ 15 N 15 N]-urea.In Experiment 1, the objective was to determine how interactions between dietary ruminally-degradable protein (RDP) level and ruminally-fermentable carbohydrate (RFC) may alter urea-N transfer to the gastrointestinal tract (GIT) and the utilization of this recycled urea-N in rapidly-growing lambs fed high N diets.The dietary factors were: 1) dry-rolled barley (DRB) vs. pelleted barley (PB) as the principal source of RFC; and 2) dietary levels of RDP of 60 vs. 70% (% of CP).Nitrogen intake, fecal and urinary N excretion increased as dietary RDP level increased; however, method of barley processing had no effect on N use.Dietary treatment had no effect on urea-N kinetics; however, endogenous production of urea-N (UER) exceeded N intake.For all diets, 0.669 to 0.742 of UER was recycled to the GIT; however, 0.636 to 0.756 of the GER was returned to the ornithine cycle.In Experiment 2, the objective was to delineate the effects of partial defaunation of the rumen on urea-N kinetics in lambs fed low or high N diets.Treatments were: 1) partial defaunation (PDFAUN) vs. faunation (FAUN); and 2) low (10%, LOW) vs. high (15%, HIGH) dietary CP.Linoleic acid-rich sunflower oil was fed as a partially-defaunating agent.Partial defaunation decreased ruminal NH 3 -N concentrations.The UER and urinary urea-N excretion (UUE) were lower, and the GER tended to be lower in PDFAUN as compared to FAUN lambs; however, as a proportion of UER, GER was higher and the proportion of recycled urea-N that was utilized for anabolism (i.e., UUA) tended to be higher in PDFAUN lambs.The UER, GER and UUE were higher in lambs fed diet HIGH; however, as a proportion of UER, GER and its anabolic use were higher in lambs fed diet LOW.In Experiment 3, the objective was to delineate how, at similar N intakes, interactions between ruminal partial defaunation and altering dietary RFC may alter urea-N kinetics and N metabolism in lambs.Treatments were: 1) PDFAUN vs.FAUN; and 2) DRB vs. PB.Urinary N excretion was lower and retained N was higher in PDFAUN compared to FAUN lambs.The UER was similar across treatments; however, the GER, expressed as absolute amounts or as a proportion of UER, UUA, and microbial N supply were higher in PDFAUN compared to FAUN lambs.As a proportion of UER, GER was higher, whereas UUE was lower in lambs fed PB compared to those fed DRB.In Experiment 4, the iii objective was to determine the effects of feeding oscillating dietary CP compared to static dietary CP concentration on N retention and in vitro urea flux across ruminal epithelia.Dietary treatments consisted of a medium CP diet (MEDIUM; 12.8% CP) or diets with oscillating CP content (OSC) fed in two different sequences i.e., 2 d of low CP (9.7% CP) followed by 2 d of high CP (16.1% CP; OSC-HIGH) or vice-versa (OSC-LOW).Ruminal epithelial tissues were collected and mounted in Ussing chambers under short-circuit conditions and the serosal-tomucosal urea flux (J sm-urea ) was measured using 14 C-urea.Although N intake was similar, retained N and microbial N supply were greater in lambs fed the OSC diets compared to those fed the MEDIUM diet.The total J sm-urea was higher in lambs fed the OSC-LOW compared to those fed the OSC-HIGH diet.Across diets, the addition of phloretin (a known specific inhibitor of facilitative urea transporter-B; UT-B) reduced J sm-urea ; however, phloretin-insensitive J sm-urea was the predominant route for transepithelial urea transfer.In summary, data presented in this thesis provide new insights that the improved N retention typically observed in defaunated ruminants and in ruminants fed oscillating dietary CP concentrations is partly mediated via increased urea-N recycling to the GIT and utilization of recycled urea-N for anabolic purposes.resolute encouragement, generous support and constructive criticism during my entire Ph.D.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.001 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.001 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".