An investigation was conducted to determine the contribution of the gastrointestinal microbiota to variation in bioefficacy of methionine sources and the interrelationship between intestinal microbiota and cereal grain type with respect to gastrointestinal physiology. Apparent gastrointestinal absorption of DL-methionine (MET) and 2-hydroxy-4-methylthiobutanoic acid (MHA-FA), post-weaning intestinal morphology, digestive physiology, mucin dynamics and digesta flow were studied in a series of experiments using conventional and gnotobiotic pigs. At 14 d of age, sow - reared conventional (CON) pigs and isolator - reared monoassociated gnotobiotic pigs (EF) were weaned to corn or wheat/barley based diets supplemented with MET or MHA-FA. At 24 d of age, after an overnight fast, pigs were fed experimental diet supplemented with 107 Bq of either 3H-L-MET or 3H-L-MHA-FA per kg of feed and chromic oxide (0.5% wt/wt). Pigs were killed 3 h after consuming the meal to collect digesta and tissue samples from the stomach and along the small intestinal (SI) length. Conventional pigs fed a wheat/barley-based diet had increased (P < 0.05) total aerobes, whereas supplementation with MHA-FA increased (P < 0.05) total aerobes and lactobacilli populations in proximal SI. Among the gnotobiotic pigs, 8 pigs (2 isolators) were monoassociated with a bacteria closely related to <i>Providencia</i> spp. and 16 pigs (4 isolators) were monoassociated with <i>Enterococcus faecium</i> (EF). Species of bacterial contaminant and diet composition did not affect residual MET or MHA-FA in digesta. Decreased (P < 0.05) apparent residual MET in digesta compared with MHA-FA in CON but not monoasscoiated pigs, along with significantly higher (P<0.05) MET associated radioactivity at 5% SI tissue suggested that microbial metabolism of MHA-FA increases its retention in small intestinal digesta and contributes in part to the lower bioefficacy of MHA-FA compared to MET. A comparison of CON and EF pigs showed that wheat/barley diets increased digesta viscosity (<i>P</i> < 0.01) and proliferating cell nuclear antigen (PCNA) expression (<i>P</i> < 0.001) and tended to decrease (<i>P</i> < 0.07) aminopeptidase N (APN) activity. Monoassociation decreased (<i>P</i> < 0.01) body weight, relative spleen weight, crypt depth, PCNA expression, caspase-3 activity, sucrase expression, total goblet cells in crypts and mucin gene expression and increased (<i>P</i> < 0.01) relative SI length, digesta viscosity, villus height, APN and sucrase activity. Interactive effects between cereal grain type and microbial status were observed only as trends (<i>P</i> < 0.1) for PCNA, Muc2, APN and sucrase suggesting these effects were mediated indirectly through microbial changes. Decreased % retained chromic oxide in digesta at all SI locations and no chromic oxide at 95% SI length in monoassociated pigs indicated slower small intestinal transit of digesta in monoassociated pigs. We successfully developed the chromic oxide microassay for estimating chromic oxide in 1/20th of original sample size (2.0 g). Results of this study indicate that microbial metabolism of MHA-FA contributes in part to the lower bioefficacy of MHA-FA compared to MET. Monoassociation had major effects on intestinal physiology whereas limited indirectly mediated effects of cereal type were observed suggesting no major influences of cereal grain type during the short early post-weaning phase.

An investigation was conducted to determine the contribution of the gastrointestinal microbiota to variation in bioefficacy of methionine sources and the interrelationship between intestinal microbiota and cereal grain type with respect to gastrointestinal physiology. Apparent gastrointestinal absorption of DL-methionine (MET) and 2-hydroxy-4-methylthiobutanoic acid (MHA-FA), post-weaning intestinal morphology, digestive physiology, mucin dynamics and digesta flow were studied in a series of experiments using conventional and gnotobiotic pigs. At 14 d of age, sow - reared conventional (CON) pigs and isolator - reared monoassociated gnotobiotic pigs (EF) were weaned to corn or wheat/barley based diets supplemented with MET or MHA-FA. At 24 d of age, after an overnight fast, pigs were fed experimental diet supplemented with 107 Bq of either 3H-L-MET or 3H-L-MHA-FA per kg of feed and chromic oxide (0.5% wt/wt). Pigs were killed 3 h after consuming the meal to collect digesta and tissue samples from the stomach and along the small intestinal (SI) length. Conventional pigs fed a wheat/barley-based diet had increased (P < 0.05) total aerobes, whereas supplementation with MHA-FA increased (P < 0.05) total aerobes and lactobacilli populations in proximal SI. Among the gnotobiotic pigs, 8 pigs (2 isolators) were monoassociated with a bacteria closely related to <i>Providencia</i> spp. and 16 pigs (4 isolators) were monoassociated with <i>Enterococcus faecium</i> (EF). Species of bacterial contaminant and diet composition did not affect residual MET or MHA-FA in digesta. Decreased (P < 0.05) apparent residual MET in digesta compared with MHA-FA in CON but not monoasscoiated pigs, along with significantly higher (P<0.05) MET associated radioactivity at 5% SI tissue suggested that microbial metabolism of MHA-FA increases its retention in small intestinal digesta and contributes in part to the lower bioefficacy of MHA-FA compared to MET. A comparison of CON and EF pigs showed that wheat/barley diets increased digesta viscosity (<i>P</i> < 0.01) and proliferating cell nuclear antigen (PCNA) expression (<i>P</i> < 0.001) and tended to decrease (<i>P</i> < 0.07) aminopeptidase N (APN) activity. Monoassociation decreased (<i>P</i> < 0.01) body weight, relative spleen weight, crypt depth, PCNA expression, caspase-3 activity, sucrase expression, total goblet cells in crypts and mucin gene expression and increased (<i>P</i> < 0.01) relative SI length, digesta viscosity, villus height, APN and sucrase activity. Interactive effects between cereal grain type and microbial status were observed only as trends (<i>P</i> < 0.1) for PCNA, Muc2, APN and sucrase suggesting these effects were mediated indirectly through microbial changes. Decreased % retained chromic oxide in digesta at all SI locations and no chromic oxide at 95% SI length in monoassociated pigs indicated slower small intestinal transit of digesta in monoassociated pigs. We successfully developed the chromic oxide microassay for estimating chromic oxide in 1/20th of original sample size (2.0 g). Results of this study indicate that microbial metabolism of MHA-FA contributes in part to the lower bioefficacy of MHA-FA compared to MET. Monoassociation had major effects on intestinal physiology whereas limited indirectly mediated effects of cereal type were observed suggesting no major influences of cereal grain type during the short early post-weaning phase.

The use of ADF as internal Marker of duodenal digesta flow was evaluated, for this the intestinal degradability of fiber was studied. Four Holstein calves (156± 33 kg), fitted with duodenal cannula T simple, and one calve fitted on the rumen, fed diet base with black oat and supplement, was used. Seven feeds were weighted on the polyester bags (7x5,5cm; 25μm) and treated at different ruminal incubation times (12, 24, 36 and 48 hours). After the respective incubations times, the bags were introduced in the duodenum of animals, recovered on the faeces and analyzed. The means of fiber fraction obtained posruminally and on the samples recovered on the faeces, were significantly different (P<0,05). The percent difference was 6,44, 2,07 e 0,90% on DM basis, for NDF, ADF and ADL, respectively. The disappearance of ADL indicated loss of particles through the pores of the bags, thereby the means were corrected for the loss of ADL, improving the regression coefficients and intercept of the regression equations, demonstrating the potential of using the ADF as an internal marker of digesta flow in ruminants. Additionally, was evaluated the duodenal digesta flow on cattle, with different markers. The means obtained from the ADF and ADL were similar, 2,025 and 2,135 kgDM/day, respectively. The n-alkanes presented low fecal recovery (C31= 63,3%; C32=46,7% e C33=75,6%), this may have contributed to the high variability of the results obtained from the n-alkanes. The n-alkane C32 overestimated the duodenal flow of DM, 3,855 kgDM/day. The ADF was useful for to measure the duodenal digesta flow, even small loss was detected, this did not prejudice the assessment. The ADF was efficient for measure digesta flow of DM, differently of the n-alkanes that overestimated (C32) and presented high variability (C31, C32 and C33). / Este estudo foi conduzido com o objetivo de avaliar o potencial do uso de componentes da fibra como marcadores internos e alcanos na estimativa do fluxo duodenal em bovinos. Para tanto foi avaliada a degradabilidade intestinal das frações fibrosas de diferentes alimentos. Foram utilizados quatro bovinos da raça holandesa dotados de cânula tipo T simples no duodeno e um bovino dotado de fistula ruminal, com dieta a base de Aveia Preta e concentrados (60:40). Foram conduzidos ensaios com sete diferentes alimentos, estes sendo submetidos a diferentes tempos de incubação ruminal, (12, 24, 36 e 48 horas). Por meio da técnica dos saquinhos móveis, foi avaliada a degradação intestinal dos alimentos. As médias das frações fibrosas obtidas pós-ruminalmente e recuperadas nas fezes diferiram significativamente de FDN, FDA e LDA (P<0,05). O desaparecimento em percentual da MS foi de 6,44, 2,07 e 0,90%, para FDN, FDA e LDA, respectivamente. No entanto a análise de regressão linear indicou altos coeficientes de determinação para todos os tempos de incubação. O desaparecimento em proporção de FDA e LDA foram estatisticamente iguais em todos os tempos de incubação (P>0,05), indicando perda de partículas pelos poros dos saquinhos. A correção dos teores de FDA, pela perda de LDA não afetou os coeficientes de determinação que permaneceram elevados. A estimativa do fluxo de duodenal de MS com a FDA e a LDA foram similares, 2,025 e 2,135 kgMS/dia, respectivamente. Os n-alcanos apresentaram baixa recuperação fecal (C31= 63,3%; C32=46,7% e C33=75,6%),o que pode ter contribuído para alta variabilidade dos resultados. O C32 superestimou os valores de fluxo duodenal de MS, sendo que fluxo médio obtido pelo C32, corrigido pela excreção fecal do alcano, foi de 3,855 kgMS/dia, enquanto o observado com o FDA foi de 2,065kgMS/dia e 2,135 kgMS/dia com base no LDA. O FDA foi eficiente para medir o fluxo duodenal de MS, , diferentemente do n-alcano dosado, o C32, que superestimou este parâmetro e, como C31 e C33, apresentou resultados com alta variabilidade.