Justificativa: Doses inadequadas de diálise estão associadas a maior morbidade e mortalidade em pacientes com uremia terminal em tratamento hemodialítico. Atualmente os métodos mais utilizados para medir a adequação da hemodiálise baseiam-se no cálculo da depuração fracional de uréia (Kt/V) e da taxa de redução da uréia (URR). Nesse estudo avaliou-se a reprodutibilidade do Kt/V e da URR e analisou-se o número aceitável de medidas mensais destes parâmetros para determinar de forma fidedigna a adequação da hemodiálise. Métodos: Avaliamos 43 pacientes clinicamente estáveis, em cinco sessões de hemodiálise (sessões 1 a 5), durante três semanas. Três diálises consecutivas na primeira semana (sessões 1, 2, 3) e duas sessões de meio de semana, nas duas semanas subseqüentes (sessões 4 e 5). Resultados: Não houve diferença entre a média dos Kt/Vs obtidos em diálises seqüenciais (1, 2 e 3) comparada a média dos Kt/Vs obtidos em diálises no meio da semana (2, 4 e 5). O mesmo aconteceu com a URR e com os coeficientes de variação do Kt/V e da URR. Também não encontramos diferença entre uma medida mensal (Kt/V 2) e três medidas mensais (média dos Kt/Vs 2, 4 e 5). O mesmo ocorreu com a URR. A diferença entre o Kt/V 2 e a média dos Kt/Vs 2, 4 e 5 foi de – 0,02 unidades e entre a URR 2 em relação a média das URRs 2, 4 e 5 foi de – 0,5%. Além disso, se fizermos apenas uma medida mensal (Kt/V 2) 80% dos pacientes estarão a uma distância de no máximo 0,16 unidades abaixo da média dos Kt/Vs 2, 4 e 5 e no máximo 0,12 unidades acima. Em relação a URR 80% dos pacientes estarão a uma distância de no máximo 4,37% abaixo da média das URRs 2, 4 e 5 e no máximo 3,37% acima. O grau de concordância entre o Kt/V 2 e a média dos Kt/Vs 2, 4 e 5 é bom para pontos de corte do Kt/V igual ou superior a 1,3. No caso da URR a concordância é boa para pontos de corte acima de 65%. Conclusão: Concluímos que nesta população de pacientes clinicamente estáveis os parâmetros de adequação da hemodiálise mostraram-se reprodutíveis não havendo necessidade de aumentar o número de medidas mensais da quantidade de diálise ofertada. / Background: Inadequate doses of dialysis are associated with higher morbidity and mortality rates for end-stage renal disease (ESRD) patients undergoing hemodialysis treatment. Most methods aimed at measuring dialysis adequacy use the calculation of fractional clearance of urea (Kt/V) and urea reduction ratio (URR). This study evaluates the reproducibility of Kt/V and URR and analyzes the acceptable number of monthly measurements of these parameters to determine hemodialysis adequacy. Methods: We evaluated 43 clinically stable patients in five hemodialysis sessions (1 to 5) along three weeks. Three consecutive sessions were carried out in the first week (1, 2, 3), while the two other studied sessions were carried out in the middle of the week at weekly intervals (4, 5). Results: There was no difference between mean Kt/V in sessions 1, 2, and 3 and in sessions 2, 4, and 5. The same was observed for URR and the coefficients of variation for Kt/V and URR. Either differences were found between one monthly measurement (2) or three monthly measurements (mean of 2, 4, and 5) for Kt/V and URR. The difference between Kt/V 2 and the arithmetic mean of Kt/Vs 2, 4, and 5 was – 0.02 units, and between URR 2 and the mean of URRs 2, 4, and 5 was – 0.5%. When only one monthly measurement (Kt/V 2) was considered, 80% of the patients presented ≤0.16 unit below or ≤0.12 above the mean of Kt/Vs 2, 4, and 5. For URR, 80% of patients presented ≤4.73% below or ≤3.37% above the arithmetic mean of URRs 2, 4, and 5. The degree of agreement between Kt/V 2 and the mean of Kt/Vs 2, 4 and 5 is good for Kt/Vs of 1.3 or higher. URR agreements are good for URR of 65% or higher. Conclusion: In this population, hemodialysis adequacy parameters were reproducible, and an increase in the number of monthly measurements seems not to be necessary.

Níveis elevados de proteína bruta (PB) na dieta de ruminantes têm sido associado com comprometimento na fertilidade devido, principalmente, a elevação da concentração do nitrogênio uréico plasmático (NUP). Objetivou-se no presente estudo avaliar o efeito do fornecimento de dietas contendo nitrogênio não-protéico (NNP) sem prévia adaptação, durante curto espaço de tempo e em diferentes fases do ciclo estral, a fêmeas bovinas superovuladas quanto à produção, qualidade e ao grau de desenvolvimento de embriões recuperados. Sessenta e oito vacas da raça Nelore com escore corporal de 7,56 e peso médio de 557,6 kg foram distribuídas em três tratamentos: controle (C), uréia antes do dia 0 (UA; fornecimento de dieta com uréia do dia -5 ao dia 0) e uréia depois do dia 0 (UD; fornecimento de dieta com uréia do dia 0 ao dia 5). As vacas foram mantidas em piquetes com pastagem de Brachiaria brizantha cv. Marandu e receberam diariamente, 3,0 kg/animal de concentrado durante 16 dias. Foram formulados dois concentrados, sendo que as dietas totais (concentrado + consumo estimado de pastagem) continham 12,0% (dieta controle) e 14,6% de PB (dieta com NNP). A diferença na PB entre as dietas foi o acréscimo de 100g/vaca/dia de uréia. Os animais foram sincronizados, superovulados e inseminados. Sete dias (dia 7) após a inseminação (dia 0), realizou-se a colheita e análise dos embriões quanto à qualidade a ao grau de desenvolvimento. Amostras de sangue foram coletadas nos dias -5, 0 e 5 para mensurações das concentrações de NUP, glicose, insulina e progesterona. Houve efeito significativo dos tratamentos sobre a concentração médias de NUP no dia -5 (C = 16,18ab, UA = 17,72a e UD = 14,47b mg/dL; P = 0,0007), no dia 0 (C = 18,95b, UA = 22,71a e UD = 21,15 ab mg/dL; P = 0,0010) e no dia 5 (C = 20,93a, UA = 19,08b e UD = 21,51a mg/dL; P = 0,0022). Quanto às concentrações de glicose, insulina e progesterona não houve efeito dos tratamentos. Não houve efeito significativo nem da inclusão da uréia e nem do momento da inclusão da uréia sobre o total de estruturas recuperadas, total de estruturas fecundadas e de embriões viáveis. Porém, houve efeito do momento de inclusão da uréia sobre a porcentagem de estruturas fecundadas em relação ao total de estruturas recuperadas (UA = 75,3 vs. UD = 50,7%) e sobre a porcentagem de embriões viáveis em relação ao total de estruturas recuperadas (UA = 73,2 vs. UD = 39,4%). O tratamento UD acarretou em menor capacidade de fecundação do oócito em relação ao tratamento UA, havendo redução de aproximadamente 32,7% na proporção de oócitos fecundados sobre o total de estruturas recuperadas deste tratamento. / High levels of crude protein (CP) in ruminant diets were associated with detrimental effect on fertility, mainly, due to the rise of plasmatic urea nitrogen (PUN) concentration. The aim of this study was to verify the effects of short term non-protein nitrogen feeding at different periods of the oestrus cycle in superovulated cows without previous adaptation on yield, quality and development degree of recovered embryos. Sixty eight Nelore cows with body condition score of 7.56 and body weight of 557.6 kg were divided in three different groups: control (C), urea before day 0 (UB; urea supply from day -5 to day 0) and urea after day 0 (UA; urea supply from day 0 to day 5). Animals were grazing in Brachiaria brizantha cv. Marandu pasture and received 3.0 kg/animal/day of concentrate during 16 days. Two concentrates were formulated and the total diets (concentrate + estimate forage intake) had 12.0% (control diet) and 14.6% of CP (NPN diet). The difference in CP between diets was the addition of 100g/cow/day of urea. Animals were synchronized, superovulated and inseminated. The embryos were collected seven days (day 7) after insemination (day 0) and quality and development degree were also evaluated. Blood samples were collected on day -5, 0 and 5 for measurement of PUN, glucose, insulin and progesterone. There was significant effect of treatments on average PUN concentration at day -5 (C = 16.18ab, UB = 17.72a and UA = 14.47b mg/dL; P = 0.0007), at day 0 (C = 18.95b, UB = 22.71a and UA = 21.15ab mg/dL; P = 0.0010) and at day 5 (C = 20.93a, UB = 19.08b and UA = 21.51a mg/dL; P = 0.0022). For glucose, insulin and progesterone there was no effect of treatments. It was observed neither effect of urea inclusion nor the moment of urea inclusion in diet on the total number of recovered structures, total number of fertilized structures and total number of viable embryos. However, it was observed effect of the moment of urea inclusion on the rate of fertilized structures in relation to the total number of recovered structures (UB = 75.3 vs. UA = 50.7%) and on the rate of viable embryos in relation to the total number of recovered structures (UB = 73.2 vs. UA = 39.4%). The UA treatment lead to lowest fertilizing oocyte capacity in relation to UB treatment with an approximate reduction of 32.7% on oocytes fertilized proportion over the total recovered structures in this treatment.

Este estudo teve como objetivo avaliar o efeito de níveis crescentes de uréia na dieta de vacas em lactação sobre a produtividade, características físico-químicas e de composição do leite, bem como composição da proteína do leite. Foram utilizadas nove vacas Holandesas em lactação, em delineamento experimental tipo quadrado latino 3X3, com 3 tratamentos, 3 períodos e 3 quadrados. O experimento teve duração total de 63 dias divididos em 3 períodos de 21 dias. Os tratamentos foram: tratamento A (controle) com dieta formulada para suprir 100% das exigências do NRC (2001) em termos de PB, proteína degradável no rúmen (PDR), proteína não degradável no rúmen (PNDR), utilizando farelo de soja como principal fonte protéica e cana-de-açúcar como volumoso; tratamento B, dieta com a inclusão de 0,75% de uréia, em substituição parcial ao farelo de soja, e tratamento C, dieta com inclusão de 1,5% de uréia, em substituição parcial ao farelo de soja. Todas as dietas foram isoenergéticas (1,53 Mcal/kg de energia líquida de lactação) e isoprotéicas (16% de proteína bruta). Não foram observadas diferenças entre os tratamentos, quando os resultados foram analisados por regressão polinomial simples, quanto a: consumo de matéria seca, produção de leite, produção de leite corrigida para 3,5%, produção de proteína, produção de gordura, produção de lactose e produção de sólidos totais e Log CCS. Também não houve influência dos tratamentos sobre pH, crioscopia, densidade e prova de resistência ao álcool. No entanto, a acidez, sofreu efeito linear decrescente (p = 0,017) em função dos níveis de uréia na dieta. Quanto à composição do leite, os teores de proteína, gordura, lactose, uréia, extrato seco total e extrato seco desengordurado não foram influenciados pelos tratamentos. A composição da proteína também não foi alterada pela inclusão de até 1,5% de uréia na dieta, não sendo observada diferença entre os tratamentos para a proteína bruta, proteína verdadeira, caseína, proteína do soro, nitrogênio não caseinoso, nitrogênio não protéico, uréia, bem como as relações proteína verdadeira: proteína bruta e caseína: proteína verdadeira. Estes resultados sugerem que o uso de até 1,5% de uréia na matéria seca da dieta não altera a capacidade de produção, as características físico-químicas e de composição do leite, bem como a composição da proteína do leite. / The aim of this study was to evaluate the effects of three different dietary levels of urea on milk yield and composition, and milk protein composition. Nine lactating Holstein cows were used in a 3X3 latin square arrangement, with 3 treatments, 3 periods of 21 days each and 3 squares. The treatments were: A) NRC-based (NRC, 2001) diet to provide 100% of crude protein (CP), as well as, rumen undegradable protein (RUP) and rumen degradable protein (RDP) requirements, by using soybean meal and sugar cane; B) 0,75% urea inclusion; partially substituting soya meal from diet C) 1,5% urea inclusion, partially substituting soya meal from diet. Energy and protein levels of treatment diets comply with NRC (2001), and were isoenergetic and isoproteic. No statistical differences were observed among treatments, when results were analyzed by simple polynomial regression in relation to dry-matter intake, milk yield, 3,5% FCM, protein and fat yield, and somatic cell count (Log SCC). Cryoscopy, pH, milk density and alcohol stability, fat, lactose, urea, total solids and solids with no fat were not influenced by treatments. The protein composition, crude protein, true protein, casein, whey protein, non-casein nitrogen, milk urea nitrogen, as well as, true protein:crude protein and casein:true protein ratios were not influenced by the substitution of soybean meal by urea in ration. Results indicate that the use of urea up to 1,5% in DM does not alter milk yield and its composition.

Made available in DSpace on 2016-05-02T13:54:18Z (GMT). No. of bitstreams: 1 EvandroFreireLemos-dissertacao.pdf: 149475 bytes, checksum: 157cfab2d31ed366f87b82fe037eb10e (MD5) Previous issue date: 2011-06-14 / The adoption of best practices for use of fertilizers has contributed to the reduction in nutrient losses and the use of protected sources of nitrogen appears to be an interesting alternative.The aim of this study was a technical and economic evaluation of the effects of different nitrogen using slow release urea compared with traditional use of urea. The experimental design was randomized blocks with seven treatments and four replications. It was demonstrated the possibility of reducing nitrogen levels when using the slow release urea can also be applied at planting. Throughout the experiment the use of conventional urea proved more economical. It was concluded that it is necessary to popularize the techniques of protection of urea, thus making the cost of fertilizer more competitive. Treatment 3, which used 100% of the nitrogen in slow release urea at sowing showed the highest yield, and the second treatment, conventional urea applied at planting 30% and 70% coverage (merged) presented the highest net revenue per hectare, considering the costs of fertilizer. / A adoção das boas práticas do uso de fertilizantes tem contribuído para a redução nas perdas de nutrientes, e a utilização de fontes de nitrogênio protegidas parece ser uma alternativa interessante. Sendo assim, o objetivo deste trabalho foi realizar uma avaliação técnica e econômica dos efeitos de diferentes doses de nitrogênio, utilizando ureia de liberação lenta comparado com uso de ureia tradicional na cultura do milho. O delineamento experimental usado foi de blocos casualizados, com sete tratamentos e quatro repetições. Ficou evidenciada a possibilidade de redução da dose de nitrogênio ao se utilizar a ureia de liberação lenta, podendo também a aplicação ser feita toda no plantio, tendo, entretanto, o uso da ureia convencional se mostrado mais econômico. O tratamento 3, em que se utilizou 100% da dose de nitrogênio com ureia de liberação lenta no plantio foi o que apresentou maior produtividade, e o tratamento 2, ureia convencional aplicada 30% no plantio e 70% em cobertura (incorporada), foi o que apresentou maior receita líquida por hectare, considerando os custos da adubação. Pode-se concluir que há necessidade da popularização das técnicas de proteção da ureia, tornando assim o custo do fertilizante mais competitivo em detrimento aos demais nitrogenados.

Nitrogen (N) is the most commonly over-applied nutrient in urban environments because of the large visual and growth increases. This over-application has led to an increase in the loss of N gas in the forms of ammonia and nitrous oxide, as well as an increase in nitrate leaching to surface and groundwater. Furthermore, excess N results in increased maintenance costs and landfill volume due to increased shoot growth from mowed clipping removal. Polymer coated urea (PCU) has proven to be an excellent source to these losses of N to the environment, but rate and timing parameters need study. A two-year field study, on sand and sandy loam soils in Provo, UT, was initiated in April 2014. Seven fertilized treatments included: urea split applied monthly; a single application of PCU (Agrium One Ap) applied in spring, a single PCU application in fall; two evenly split applications in spring and late summer; and three evenly split applications in spring, late summer, and late fall. These were compared to an untreated control. In addition the two application of PCU also had reduced rates of half and three-quarters, in addition to the full rate. Height and verdure measurements were taken on a weekly basis, along with periodic visual and biomass readings. All fertilized treatments resulted in a significant response to N as compared to the control. The single annual application treatments had significantly greater shoot growth during the weeks immediately after application and a significant reduction in verdure months later and, therefore, were unacceptable for consumer recommendation. Two applications of PCU, either at the three-quarter or full rates, were nearly identical in all measurements as compared to the spoon feeding of urea applied monthly. The half rate of two applications showed signs of inadequate N. Three applications of PCU was identical to two and, therefore, not recommended. This study shows two applications of PCU at the three-quarter rate is equally effective as spoon feeding the N. Doing so would result in less labor for fertilization. Further work is needed to evaluate other timing approaches for a single annual application, as well as long term effects of a reduced rate of N.

Plants require N to complete their life cycle. Without adequate concentration of N, crops will not produce their potential yields. For turfgrass systems, N fertilizer application allows for the maintenance of functional, aesthetic, and recreational properties. However, fertilizer mismanagement is common and leads to N pollution in the environment. Controlled-release and slow-release fertilizers can enhance nitrogen (N)-use efficiency, reduce N pollution, minimize the need for repeated fertilizer applications, and reduce turfgrass shoot growth and associated costs. In order to evaluate the effectiveness of these fertilizers in the Intermountain West, research is needed. The timing of N release was evaluated for seven urea fertilizers: uncoated, sulfur coated (SCU), polymer-sulfur coated (PSCU), and four polymer-coated (PCU) with release timings of 45, 75, 120, and 180 d estimated release. These products were placed on bare soil, a Kentucky bluegrass (Poa pratensis L.) thatch layer, and incorporated into soil. These three placement treatments were replicated to allow for enough samples to be placed in two locations. The first was outside in a field to represent field conditions with diurnal fluctuating temperatures and the second was placed in a storage facility to replicate laboratory conditions with static diurnal temperatures. The PCU prills incorporated into soil under field conditions generally released N over the estimated release period. However, when applied to bare soil or thatch, N from PCU had 80% or greater N release by 35 d after application regardless of expected release time. Fertilizers under laboratory conditions had minimal N release despite having similar average daily temperatures, suggesting that fluctuating temperatures impact N release. The PSCU and SCU treatments were no different from uncoated urea, showing no slow release properties for this particular product. Spring-applied N fertilizer trials were conducted over two years to determine the optimal N rate for Kentucky bluegrass. Similar PCU120 products were applied at 50, 75, and 100% of the recommended full rate, while also being compared to an unfertilized control and urea applied either all at once or split monthly. Spring-applied PCU showed minimal initial N response while urea applied all at once resulted in an initial spike of N uptake. Once PCU began to release N, there was minimal difference for all rates compared to urea split monthly for biomass growth, verdure, and shoot tissue N. Although at the 50% rate, there were a few sampling dates with slower growth and lower verdure. The decrease in verdure at this low rate was slight, and it is recommended that PCU could be applied effectively at a reduced rate between 50 and 75%. Although for better results, additional quick release N is required to compensate for early season lag in N release.

Källsorterande avloppssystem gör att resurserna i olika avloppsflöden kan tas tillvara. Särskilt klosettvatten innehåller näringsämnen som är viktiga att föra tillbaka till jordbruket. I Södertälje finns en anläggning som behandlar klosettvatten från slutna tankar och produkten används som gödsel. Hygieniseringen sker i två steg, först våtkompostering som höjer temperaturen och sedan ammoniakhygienisering genom tillsats av urea. För att våtkomposteringen ska fungera effektivt är det viktigt att klosettvattnet är så koncentrerat som möjligt, så att energiinnehållet är högt. Av denna anledning bör vakuumtoalett eller annan extremt snålspolande toalett användas. Våtkomposten i Södertälje har varit i drift sedan 2012 och det här examensarbetet har syftat till att utvärdera anläggningen. Det första målet var att kvantifiera massflöden av kväve och fosfor. Dock visade sig variationen i underlaget vara så stor att inga säkra slutsatser kunnat dras utifrån tillgängliga data. Osäkerheten visas med de 90% konfidensintervallen för in- och utgående totalmängder kväve och fosfor för åren 2014–2021. Ingående mängder upp­skattades till 0–170 kg P och 370–6200 N medan utgående mängder uppskattades till 60–280 kg P och 4000–23000 kg N. Ingående närings-koncentrationer tyder på att klosettvattnet i genomsnitt kommit från runt 100 personer per år, dock råder en stor variation och osäkerhet. Det andra målet var att uppskatta gasutsläpp från anläggningen. Osäkerheten i underlaget var som sagt stor vilket syns med det 90% konfidensintervallet som gick från -9 ton till 11 ton för kvävehaltiga gaser och från -4,4 ton till 20 ton för koldioxid, totala mäng-der utsläpp under åren 2014–2021. Resultat från litteraturstudien tyder på att utsläpp av metan och lustgas bör vara väldigt låga efter att urea har tillsatts vid behandlingen. Det är viktigt att lagring av produkten sker täckt för att förhindra ammoniakavgångar. Det tredje målet var att undersöka möjligheter att behandla andra substrat på våtkomposten, då den har kapacitet att ta emot mer material. Både säkerställande av leverans från slutna tankar samt anslutning av latrin från koloniföreningar har identifierats ha stor potential att öka kvantitet och kvalitet på inkommande substrat. Hantering av latrin­tunnor kräver däremot investering i en mottagningsanordning och om det skulle vara av intresse behöver alternativ och kostnader undersökas vidare. Latrin från koloniföreningar som samlas upp i slutna tankar, vilket är fallet hos två föreningar i kommunen, kan enkelt tillföras våtkomposten och bedöms kunna öka TS-halten vilket gör våtkomposteringen mer effektiv. Som sista del i arbetet har en provtagningsplan tagits fram för kontroll av latrin uppsamlat i slutna tankar. Flertalet aktörer är inblandade i anläggningen och ett kontinuerligt arbete krävs för att systemet ska fungera tillfredsställande. Det är därför av största vikt att de olika aktörerna både har tydliga rutiner och ett nära samarbete.

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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 [15N15N]-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 NH3-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 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-to-mucosal urea flux (Jsm-urea) was measured using 14C-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 Jsm-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 Jsm-urea; however, phloretin-insensitive Jsm-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.

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 [15N15N]-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 NH3-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 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-to-mucosal urea flux (Jsm-urea) was measured using 14C-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 Jsm-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 Jsm-urea; however, phloretin-insensitive Jsm-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.