Estrous synchronization and artificial insemination (ESAI) are reproductive technologies that cattlemen can use to improve the reproductive performance of their herds. Controlling the gender ratio of the calf-crop can also improve the opportunity for increased revenue and profit. Producers are able to shift and/or control the gender ratio of their calf crop by incorporating sex-sorted semen into their AI programs. However, decreased conception rates to AI have been previously observed when sex-sorted semen was used in comparison to conventional semen of the same sires. The objective of the first study was to determine if conception rates will differ in females inseminated with conventional semen or SexedULTRA™ sex-sorted semen when estrus is synchronized using an industry-standard, 7-d CO-Synch + Controlled Internal Drug Release (CIDR) protocol for fixed-time artificial insemination (FTAI). The objective of the second study was to determine if conception rate to FTAI differs between SexedULTRA™ sex-sorted and conventional semen when yearling beef heifers are synchronized using a 14-d controlled internal drug release (CIDR) - PGF2α (PGF) protocol modified to optimize the control of ovulation and timing of insemination.

Orientador: Ariovaldo Pereira da Cruz-Neto / Banca: Denis Otavio Vieira de Andrade / Banca: Elisabeth Spinelli de Oliveira / Banca: Thomas Puettker / Banca: Ricardo Siqueira Bovendorp / Resumo: O uso de conceitos e metodologia da fisiologia para análise de problemas conservacionistas tem um longo histórico, e sua abordagem vai além de uma descrição de padrões de respostas, incluindo também a compreensão detalhada dos fatores mecanísticos subjacentes aos problemas da conservação. A fragmentação e a degradação do habitat resultam em mudanças no ambiente físico, que afetam diretamente parâmetros fisiológicos associados ao balanço hídrico. Animais que habitam esses ambientes altamente modificados podem estar submetidos a um estresse hídrico, e para estes animais o uso de parâmetros do balanço hídrico como medida da capacidade fisiológica da manutenção da homeostase é de grande importância. Estudos dos efeitos da fragmentação da Mata Atlântica sobre a abundância e riqueza de espécies de roedores mostram a existência de respostas diferencias à fragmentação. A presente tese aborda este padrão de respostas sob uma ótica integrativa, através da análise dos parâmetros associados à manutenção do balanço hídrico, e com o objetivo de fornecer evidências sobre as possíveis causas mecanísticas destas respostas. Para isso utilizamos um clássico protocolo de privação de água, somado à avaliação de efeitos da temperatura e à comparação entre diferentes populações de habitats com características climáticas diferentes. Seus resultados sugerem que as espécies Akodon montensis, Euryoryzomys russatus e Oligoryzomys nigripes possuem diferentes tolerâncias à privação de água, e que esta diferença pode estar relacionada à plasticidade fisiológica inerente a cada espécie. A análise dos componentes envolvidos no balanço hídrico evidenciou diferenças entre A. montensis e E. russatus, tendo a primeira apresentando maior plasticidade dos parâmetros avaliados, resultando em maior tolerância à privação de água. Somada à privação de água, a elevação da temperatura induziu uma... / Abstract: The use of concepts and metodologies of Phisiology to analise conservation issues has long history, and its approach goes further than describing response patterns, including also detailed comprehention of the mechanistic factors underlying conservations problems. Fragmentation and degradation of habitat result in changes on the physical environment, which directly affect physiological traits assotiated with water balance. Animals that inhabit these highly modified environments might be under water stress, and for those animals, using traits of water balance as a measure of physiological capacity for maintening homeostasis is of great value. Studies of the effects of the Atlantic Forest fragmentation on the abundance and richness of rodent species show the existence of differential response to fragmentation. This thesis addresses these patterns of responses under an integrative perspective through the analisis of parameters associated to the maintenence of water balance, and in order to provide evidences about the possible mechanistics causes of these responses. For that we used a classical protocol of water deprivation, added to the effects of temperature and to the comparison among different populations from habitats with distinct climate characteristics. The results suggest that the species Akodon montensis, Euryorysozomys russatus and Oligoryzomys nigripes hold different tolerances to water deprivation, and these differences might be related to the physiological plasticity intrinsic of each species. The analisis of the components involved in water balance revealed differences between A. montensis and E. russatus, the first one presenting a higher plasticity on the evaluated traits, which result on higher tolerance to water deprivation. Added to water deprivation, the rising of temperature induced a series of alterations on the evaluated parameters in A. montensis, imposing higher pressure on the water balance maintenance, triggering ... / Doutor

Orientador: Denis Otavio Vieira de Andrade / Banca: Braz Titon Junior / Banca: Guilherme Gomes / Resumo: Devido à alta permeabilidade da pele e a ectotermia, anfíbios terrestres são confrontados por compromissos envolvendo o balanço de água e a regulação da temperatura corpórea. O modo como tais compromissos são acomodados, sobre uma extenção de temperaturas e estados de hidratação, influencia importantemente o comportamento e a ecologia desses animais. Nesse contexto, usando o anfíbio terrestre Rhinella schneideri como organismo modelo, os objetivos do presente estudo foram duplos. Primeiramente, nós determinamos como a sensibilidade termal de uma característica ecologicamente relevante - a locomoção - é afetada pela desidratação. Além disso, nós examinamos os efeitos dos mesmos níveis de desidratação na preferência termal e na tolerância termal. A medida que a desidratação se torna mais severa, as temperaturas ótimas para o desempenho locomotor diminuíram e a amplitude de temperaturas para um desempenho próximo ao máximo se estreitou. Semelhantemente, a desidratação foi acompanhada por uma diminuição da amplitude de tolerância termal. Tal declínio foi causado pelo aumento da temperatura crítica mínima e pela diminuição da temperatura crítica máxima, com este último mudando de modo mais acentuado. Em geral, nossos resultados mostram que os efeitos negativos da desidratação no desempenho comportamental e na tolerância termal são, ao menos parcialmente, amenizados pelo simultâneo ajuste na preferência termal. Nós discutimos algumas potenciais implicações dessa observação para a ... (Resumo completo, clicar acesso eletrônico abaixo) / Abstract: Due to their highly permeable skin and ectothermy, terrestrial amphibians are challenged by compromises between water balance and body temperature regulation. The way in which such compromises are accommodated, under a range of temperatures and dehydration levels, impact importantly the behavior and ecology of amphibians. Thus, using the terrestrial toad Rhinella schneideri as a model organism, the goals of the present study were two-fold. First, we determined how the thermal sensitivity of a centrally relevant trait - locomotion - was affected by dehydration. Secondly, we examined the effects of the same levels of dehydration on thermal preference and thermal tolerance. As dehydration becomes more severe, the optimal temperature for locomotor performance was lowered and performance breadth narrower. Similarly, dehydration was accompanied by a decrease in the thermal tolerance range. Such a decrease was caused by both, an increase in the critical minimal temperature and a decrease in the thermal maximal temperature, with the latter changing more markedly. In general, our results show that the negative effects of dehydration on behavioral performance and thermal tolerance are, at least partially, counteracted by concurrent adjustments in thermal preference. We discuss some of the potential implications of this observation for the conservation of anuran amphibians / Mestre

Made available in DSpace on 2016-02-05T18:30:06Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-11-09. Added 1 bitstream(s) on 2016-02-05T18:34:13Z : No. of bitstreams: 1 000857512_20161109.pdf: 979062 bytes, checksum: 37d22728378d7afa23a2f782c4fc9e55 (MD5) Bitstreams deleted on 2016-11-16T11:41:26Z: 000857512_20161109.pdf,. Added 1 bitstream(s) on 2016-11-16T12:24:08Z : No. of bitstreams: 1 000857512.pdf: 2770993 bytes, checksum: 39e42918602435a75b2e51bde4e532bc (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / O uso de conceitos e metodologia da fisiologia para análise de problemas conservacionistas tem um longo histórico, e sua abordagem vai além de uma descrição de padrões de respostas, incluindo também a compreensão detalhada dos fatores mecanísticos subjacentes aos problemas da conservação. A fragmentação e a degradação do habitat resultam em mudanças no ambiente físico, que afetam diretamente parâmetros fisiológicos associados ao balanço hídrico. Animais que habitam esses ambientes altamente modificados podem estar submetidos a um estresse hídrico, e para estes animais o uso de parâmetros do balanço hídrico como medida da capacidade fisiológica da manutenção da homeostase é de grande importância. Estudos dos efeitos da fragmentação da Mata Atlântica sobre a abundância e riqueza de espécies de roedores mostram a existência de respostas diferencias à fragmentação. A presente tese aborda este padrão de respostas sob uma ótica integrativa, através da análise dos parâmetros associados à manutenção do balanço hídrico, e com o objetivo de fornecer evidências sobre as possíveis causas mecanísticas destas respostas. Para isso utilizamos um clássico protocolo de privação de água, somado à avaliação de efeitos da temperatura e à comparação entre diferentes populações de habitats com características climáticas diferentes. Seus resultados sugerem que as espécies Akodon montensis, Euryoryzomys russatus e Oligoryzomys nigripes possuem diferentes tolerâncias à privação de água, e que esta diferença pode estar relacionada à plasticidade fisiológica inerente a cada espécie. A análise dos componentes envolvidos no balanço hídrico evidenciou diferenças entre A. montensis e E. russatus, tendo a primeira apresentando maior plasticidade dos parâmetros avaliados, resultando em maior tolerância à privação de água. Somada à privação de água, a elevação da temperatura induziu uma... / The use of concepts and metodologies of Phisiology to analise conservation issues has long history, and its approach goes further than describing response patterns, including also detailed comprehention of the mechanistic factors underlying conservations problems. Fragmentation and degradation of habitat result in changes on the physical environment, which directly affect physiological traits assotiated with water balance. Animals that inhabit these highly modified environments might be under water stress, and for those animals, using traits of water balance as a measure of physiological capacity for maintening homeostasis is of great value. Studies of the effects of the Atlantic Forest fragmentation on the abundance and richness of rodent species show the existence of differential response to fragmentation. This thesis addresses these patterns of responses under an integrative perspective through the analisis of parameters associated to the maintenence of water balance, and in order to provide evidences about the possible mechanistics causes of these responses. For that we used a classical protocol of water deprivation, added to the effects of temperature and to the comparison among different populations from habitats with distinct climate characteristics. The results suggest that the species Akodon montensis, Euryorysozomys russatus and Oligoryzomys nigripes hold different tolerances to water deprivation, and these differences might be related to the physiological plasticity intrinsic of each species. The analisis of the components involved in water balance revealed differences between A. montensis and E. russatus, the first one presenting a higher plasticity on the evaluated traits, which result on higher tolerance to water deprivation. Added to water deprivation, the rising of temperature induced a series of alterations on the evaluated parameters in A. montensis, imposing higher pressure on the water balance maintenance, triggering ... / FAPESP: 08/57687-0 / CNPq: 158975/2011-1

Made available in DSpace on 2016-12-09T13:52:22Z (GMT). No. of bitstreams: 0 Previous issue date: 2015-11-09. Added 1 bitstream(s) on 2016-12-09T13:55:27Z : No. of bitstreams: 1 000857512.pdf: 2770993 bytes, checksum: 39e42918602435a75b2e51bde4e532bc (MD5) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / O uso de conceitos e metodologia da fisiologia para análise de problemas conservacionistas tem um longo histórico, e sua abordagem vai além de uma descrição de padrões de respostas, incluindo também a compreensão detalhada dos fatores mecanísticos subjacentes aos problemas da conservação. A fragmentação e a degradação do habitat resultam em mudanças no ambiente físico, que afetam diretamente parâmetros fisiológicos associados ao balanço hídrico. Animais que habitam esses ambientes altamente modificados podem estar submetidos a um estresse hídrico, e para estes animais o uso de parâmetros do balanço hídrico como medida da capacidade fisiológica da manutenção da homeostase é de grande importância. Estudos dos efeitos da fragmentação da Mata Atlântica sobre a abundância e riqueza de espécies de roedores mostram a existência de respostas diferencias à fragmentação. A presente tese aborda este padrão de respostas sob uma ótica integrativa, através da análise dos parâmetros associados à manutenção do balanço hídrico, e com o objetivo de fornecer evidências sobre as possíveis causas mecanísticas destas respostas. Para isso utilizamos um clássico protocolo de privação de água, somado à avaliação de efeitos da temperatura e à comparação entre diferentes populações de habitats com características climáticas diferentes. Seus resultados sugerem que as espécies Akodon montensis, Euryoryzomys russatus e Oligoryzomys nigripes possuem diferentes tolerâncias à privação de água, e que esta diferença pode estar relacionada à plasticidade fisiológica inerente a cada espécie. A análise dos componentes envolvidos no balanço hídrico evidenciou diferenças entre A. montensis e E. russatus, tendo a primeira apresentando maior plasticidade dos parâmetros avaliados, resultando em maior tolerância à privação de água. Somada à privação de água, a elevação da temperatura induziu uma... / The use of concepts and metodologies of Phisiology to analise conservation issues has long history, and its approach goes further than describing response patterns, including also detailed comprehention of the mechanistic factors underlying conservations problems. Fragmentation and degradation of habitat result in changes on the physical environment, which directly affect physiological traits assotiated with water balance. Animals that inhabit these highly modified environments might be under water stress, and for those animals, using traits of water balance as a measure of physiological capacity for maintening homeostasis is of great value. Studies of the effects of the Atlantic Forest fragmentation on the abundance and richness of rodent species show the existence of differential response to fragmentation. This thesis addresses these patterns of responses under an integrative perspective through the analisis of parameters associated to the maintenence of water balance, and in order to provide evidences about the possible mechanistics causes of these responses. For that we used a classical protocol of water deprivation, added to the effects of temperature and to the comparison among different populations from habitats with distinct climate characteristics. The results suggest that the species Akodon montensis, Euryorysozomys russatus and Oligoryzomys nigripes hold different tolerances to water deprivation, and these differences might be related to the physiological plasticity intrinsic of each species. The analisis of the components involved in water balance revealed differences between A. montensis and E. russatus, the first one presenting a higher plasticity on the evaluated traits, which result on higher tolerance to water deprivation. Added to water deprivation, the rising of temperature induced a series of alterations on the evaluated parameters in A. montensis, imposing higher pressure on the water balance maintenance, triggering ... / FAPESP: 08/57687-0 / CNPq: 158975/2011-1

Degenerative joint disease, or osteoarthritis, is a major cause of lameness and morbidity in horses, humans, and dogs. There are no truly satisfactory cures for this widespread problem and current treatments all have limitations or unwanted side effects. New cell-based strategies to repair joint surface lesions have generated a high level of interest, but have yet to achieve the full restoration of articular cartilage structure and function. Currently used therapy cells include autologous chondrocytes and adult mesenchymal cells such as bone marrow derived cells and adipose derived cells. Unfortunately, the resultant repair tissue is biomechanically inferior fibrocartilage. A critical gap in knowledge in this regard is a limited understanding of the specific cellular phenotype of normal, robust articular chondrocytes. This thesis examines the global mRNA transcriptome of equine articular cartilage to test the hypothesis that adult articular chondrocytes have a unique gene expression profile. In the first part of the study, RNA-sequencing was used to compare the mRNA transcriptome of normal adult articular cartilage with five other cartilaginous tissues. From these comparisons, locus level gene expression and alternative splicing patterns have been identified that clearly distinguish articular cartilage. In the second part of the study, fetal (interzone, cartilage anlagen chondrocytes, dermal fibroblasts) and adult (bone marrow derived, adipose derived, articular chondrocytes, dermal fibroblasts) primary cells were grown in culture and stimulated to differentiate into chondrocytes. The chondrogenic differentiation potential as assessed by matrix proteoglycan and the expression of cartilage biomarker genes was highly variable among cell types. Together, these results advance our understanding of the specific phenotype of articular chondrocytes and the potential of prospective therapeutic progenitor cells to differentiate into articular chondrocytes. This new knowledge will improve efforts to optimize cell-based therapies for osteoarthritis and the repair of joint cartilage lesions.

The mare experiences a transient innate immune response to breeding, the resolution of which is crucial for optimal fertility. The majority of mares are able to modulate this inflammation in a timely fashion, but a subpopulation exists which fail to do so and are considered susceptible to persistent breeding-induced endometritis (PBIE). Seminal plasma has been shown to modulate aspects of this inflammation. Recently, two seminal plasma proteins have garnered interest for their immune modulating properties: cysteine-rich secretory protein-3 (CRISP-3) and lactoferrin. These proteins have been found to alter the binding between sperm and neutrophils based on sperm viability in vitro, but minimal work has evaluated their effect on endometrial mRNA expression of cytokines and inflammation in response to breeding. Experiments were performed to analyze the expression of equine CRISP-3. Found to be primarily synthesized in the ampulla of the vas deferens and to a lesser extent in the vesicular gland, CRISP-3 expression was only seen in the postpubertal stallion. Due to the effect of sperm viability on protein function in vitro, varying sperm populations were analyzed for their effect on gene expression in the uterus. It was determined that viable sperm suppressed the gene expression of the inflammatory modulating cytokine interleukin-6 (IL-6) in comparison to dead sperm. Next, the effect of CRISP-3 and lactoferrin on endometrial gene expression in the normal and susceptible mare was investigated. Neither protein had a significant effect on the mRNA expression of inflammatory cytokines in the normal mares at six hours post-breeding. In contrast, lactoferrin was found to significantly suppress the expression of the pro-inflammatory cytokine tumor necrosis factor (TNF)-α in susceptible mares. Due to this, lactoferrin was further analyzed as an immunomodulant for the treatment of PBIE. Susceptible mares were infused with varying doses of lactoferrin at six hours post-breeding. Although not in a dose-dependent fashion, lactoferrin was found to decrease both fluid retention and neutrophil migration, in addition to suppressing the expression of the pro-inflammatory cytokine interferon gamma (IFNγ) and increasing the gene expression of the anti-inflammatory cytokine interleukin-1 receptor antagonist (IL-1RN). In conclusion, CRISP-3 expression occurs in secretory aspects of the male reproductive tract, and appears to be up regulated after sexual maturation. Viability of spermatozoa affects the immune response to breeding and should be taken into consideration for experimental design and interpretation of data. The seminal plasma proteins CRISP-3 and lactoferrin have minimal effect on endometrial gene expression in normal mares, but lactoferrin suppresses the expression of TNF in susceptible mares. Finally, lactoferrin was found to function as a potent anti-inflammatory for the persistent inflammation seen in susceptible mares when administered post-breeding. This protein should be further investigated as a potential therapeutic for the treatment of persistent breeding-induced endometritis.

Made available in DSpace on 2015-03-26T13:46:45Z (GMT). No. of bitstreams: 1 texto completo.pdf: 246842 bytes, checksum: f7b7371c8cb299837b636e055567a1b8 (MD5) Previous issue date: 2005-03-02 / This trial was carried out to evaluate the effect of periods of urine and feces collection on urinary excretion of creatinine, urea and purine derivatives, absorbed purine, microbial nitrogen compounds production (Nmic), apparent digestibility of dry matter (DM), organic matter (OM), crude protein (CP), ether extract (EE), neutral detergent fiber (NDF) and nonfiber carbohydrates (CNF) and total digestible nutrients contents (TDN) of Nelore bovines four categories (heifers, steers, bulls and lactating cows) fed 25 or 50% concentrate, total dry matter basis. The plasma N-urea concentrations (NUP) were evaluated and the Nmic obtained in urine spot samples was compared with that of total collection. The experiment was divided in two experimental periods of 28 days each, when the feces and urine total collection were performed at 22nd and 28th day of each experimental period. Feces were colleted directly from the floor after excretion and the urine was obtained using catheters in females and funnels in males. A 25% concentrate-based diet was fed to the animals in the first period and a 50% concentrate-based diet in the second one, all of them with 12% CP. Sixteen Nelore bovines, under feedlot, housed in individual pens, were assigned to a completely randomized design, in a split plot scheme, where the treatments were represented by the plots (2 x 4 factorial scheme), with two levels of concentrate (25 or 50%) and four Nelore categories, and the split plots were represented by the urine collections. The comparisons for digestibility evaluation were made by regression analyses, that were performed considering 4 days of feces collection of each period. The equations were obtained by comparing the nutrients digestibility referent to one (24h), two (48h) or three days (72h) compared to four days (96h of collection). Comparison with six days of total feces collection, using equations (second experimental period [50% concentrate]) was considered reference (144h total feces collection). No interaction (P>0.05) among concentrate levels, Nelore categories and collection days for the urinary volume, the creatinine excretion and Nmic production was observed. Urinary volume was not affected (P>0.05) by the concentrate levels and collection days, but significant effect (P<0.05) was observed for cows. Creatinine excretion was not affected (P>0.05) by treatments and collection days, considering average of 27.1 mg/kg0.75. Absorbed purines and microbial nitrogen compounds production were also not influenced (P>005) by the treatments and collection days. Nmic production estimated by the urinary spot collection differed (P>0.05) neither from that obtained by total collection total, nor among the concentrate levels and Nelore categories. No significant difference (P>0.05) was observed for any evaluated digestibility and TDN contents during the total feces collection period. The results suggest that the coefficients of variation decresed as the period of collection days increased. Considering the results of creatinine excretion and of microbial protein production, it was concluded that a 24-h period is enough for researchs with Nelore, independently of the category, and that urinary spot sample collection can be used to estimate microbial protein production in all Nelore bovines (heifers, steers, bulls and lactating cows). Total feces collection from 1 to 6 days to evaluate nutrients apparent digestibility are precise, but better results could be obtained by increasing the collection period. / O presente trabalho foi conduzido com o objetivo de avaliar o efeito da duração do período de coletas de urina e de fezes sobre a excreção urinária de creatinina, de uréia e de derivados de purinas, as purinas absorvidas, a produção de compostos nitrogenados microbianos (Nmic), as digestibilidades aparentes da matéria seca (MS), matéria orgânica (MO), proteína bruta (PB), extrato etéreo (EE), fibra em detergente neutro (FDN) e de carboidratos não-fibrosos (CNF) e os teores de nutrientes digestíveis totais (NDT) em Nelores de quatro categorias (novilhas, machos castrados, machos inteiros e vacas em lactação) alimentados com 25 ou 50% de concentrado na base da matéria seca total das dietas. Avaliou-se ainda as concentrações de N-uréia plasmática (NUP) e comparou-se também a produção de Nmic obtida em amostras spot de urina com aquela da coleta total. O experimento foi conduzido em dois períodos experimentais com duração de 28 dias cada, sendo as coletas totais de urina e de fezes efetuadas do 22o ao 28o dias de cada período experimental. As fezes foram retiradas do piso imediatamente após excreção e a urina obtida com sondas em fêmeas e funis nos machos. Utilizou-se dieta com 25% de concentrado no primeiro período e com 50% no segundo experimental. Todas as dietas continham aproximadamente 12% de PB. Utilizaram-se 16 animais da raça Nelore, mantidos em confinamento, alojados em baias individuais, distribuídos em delineamento inteiramente casualizado, em esquema de parcelas subdivididas, tendo nas parcelas os tratamentos em esquema fatorial 2 x 4, sendo dois níveis de concentrado (25 ou 50%) e quatro categorias de Nelores e nas subparcelas os seis dias de coletas de urina. Já para a avaliação das digestibilidades, as comparações foram feitas através de análises de regressão, que foram efetuadas considerando quatro dias de coletas de fezes em cada período, sendo as equações obtidas sempre comparando as digestibilidades dos nutrientes referentes a um dia (24 h), 2 dias (48 h) ou 3 dias (72 h) em relação aos 4 dias (96 h de coleta). Foram feitas também comparações através de equações, utilizando os seis dias de coleta total de fezes, referentes ao segundo período experimental (50% de concentrado), sendo nesse caso utilizado como referência os seis dias de coleta total (144 h de coleta total de fezes). Não houve interação (P>0,05) entre níveis de concentrado, categorias de Nelore e dias de coleta para o volume urinário, a excreção de creatinina e a produção de Nmic. O volume urinário não foi influenciado (P>0,05) pelos níveis de concentrado e dias de coleta, contudo foi significativamente maior (P<0,05) para as vacas. A excreção de creatinina não foi afetada (P>0,05) pelos tratamentos e dias de coletas, observando-se média de 27,1 mg/kg0,75. As purinas absorvidas e a produção de compostos nitrogenados microbianos também não foram influenciadas (P>0,05) pelos tratamentos e dias de coleta. A produção de Nmic estimada através de amostra spot de urina não diferiu (P>0,05) daquela obtida pela coleta total, nem entre os níveis de concentrados e categorias de Nelore. Não houve diferença significativa (P>0,05) para nenhuma das digestibilidades avaliadas e também para os teores de NDT entre os dias de coleta total de fezes, contudo, observou-se que os coeficientes de variação diminuíram à medida que se aumentou o número de dias de coleta. Concluiu-se considerando as respostas obtidas para excreção de creatinina e a produção de proteína microbiana, que um período de coletas de urina de 24 horas é suficiente para trabalhos com Nelores, independente de serem novilhas, machos castrados ou inteiros e vacas em lactação e que a coleta de amostra spot de urina também pode ser utilizada para estimar a produção de proteína microbiana em novilhas, machos inteiros ou castrados e vacas lactantes da raça Nelore. Concluiu-se também que para avaliar a digestibilidade aparente dos nutrientes, coletas totais de fezes feitas durante um a seis dias são exatas. Contudo, a precisão é melhorada com o aumento dos dias de coleta.