Simulation of the nutrient dynamics in the gastrointestinal tract: application and validation of a mathematical model for grazing cattle

[摘要] - The objective of the present work was to validate the ruminal and post-ruminal nutrient dynamics and the ruminal microbial growth predictions, by using the equations of the Cornell system. The experiment was carried out during the rainy and dry seasons of the 1996 year, in a natural pasture area situated in the county of Viçosa (MG). Esophageally, ruminally and abomasally cannulated steers were used during two experimental periods within each season, and external markers (Cr2O3 and Eu) were used to estimate the intake and the ruminal digesta passage rate. The total nitrogen and the bacterial nitrogen flows, total and structural carbohydrates digested in the rumen, and the total of digestible nutrients contents were determined. These variables were also predicted from the model described in the Cornell system to validate its estimates. It was verified that the model was sensitive to the passage rate estimates, overestimated (12.38%) the bacterial nitrogen flow to the abomasum, and underestimated (70.64%) the structural carbohydrates availability in the rumen. The correction based on .02 h-1 passage rate in the estimates calculation resulted in an overestimation increase of the bacterial N flow (28.66%) due to the greatest structural carbohydrate degradation, whose estimates remained underestimated in 21.55%. The dry matter intake reduction was better correlated with the indigestible NDF than NDF contents itself, and it should be emphasized that the daily intake capacity of this fraction was 0.6% of the live weight and it did not differ between seasons.

[学科分类] 兽医学

[关键词] digestion;mathematical models;ruminants;tropical pastures     IntroduçãoA representação da essência de determinada realidade mediante a utilização de meios artificiais;com a finalidade de obter informações relativas a determinado evento ou conjunto de eventos que;isolado ou simultaneamente;podem ocorrer dentro dos limites que caracterizam o objeto de estudo;consiste no que se pode denominar de simulação de sistemas