Fracionamento dos carboidratos e cinética de degradação in vitro da fibra em detergente neutro da extrusa de bovinos a pasto

Abstract

RESUMO -Os objetivos do presente trabalho foram a caracterização e a determinação das estimativas dos parâmetros relativos à cinética de degradação ruminal dos carboidratos, em amostras de extrusa de animais mantidos em pastagem natural da Zona da Mata (MG), nas estações chuvosa e seca do ano. Para obtenção de amostras representativas, foram usados quatro animais fistulados no esôfago durante dois períodos experimentais na estação chuvosa, e três destes animais por dois períodos experimentais na estação seca, do ano de 1996. Foi efetuado o fracionamento dos carboidratos de acordo com o sistema Cornell e determinadas as taxas de degradação da fibra em detergente neutro (FDN), a partir dos perfis de degradação in vitro deste componente. Foram determinadas as frações potencialmente degradável (B 2 ) e indegradável (C) da FDN, corrigida para proteína e cinzas, e as taxas de latência dinâmica, degradação e crescimento específico dos microrganismos, a partir da fração B 2 , além dos coeficientes de degradabilidade e do efeito de repleção ruminal da FDN. Observou-se que os carboidratos não-estruturais compreenderam pequena fração dos carboidratos totais nas amostras do pasto, em ambas as estações. Os carboidratos estruturais foram responsáveis pelo aumento no teor de carboidratos totais da extrusa, com a mudança da estação chuvosa para a estação seca; contudo, por causa do aumento da fração C e da menor taxa de crescimento específico dos microrganismos durante a estação seca, foi possível notar redução da degradabilidade e aumento do efeito de repleção ruminal da FDN da extrusa.Palavras-chave: carboidratos estruturais e não-estruturais, pastos tropicais, ruminantes Carbohydrate Fractionation and Kinetic of the Neutral Detergent Fiber In VitroDegradation of the Extrusa from Grazing Cattle ABSTRACT -The objectives of the present work were to characterizate and determinate the parameters estimates related to the ruminal degradation kinetics of the carbohydrates in extrusa samples from animals maintained in a natural pasture of the Zona da Mata (MG) region, during the rainy and dry seasons of the year. To obtain representative samples, four esophageal fistulated steers were used in two experimental periods during the rainy season, and three of these animals were used in two experimental periods during the dry season, in the year of 1996. The carbohydrate fractionation according to the Cornell system was done, and the neutral detergent fiber (NDF) degradation rates were obtained from the in vitro degradation profiles of this component. The potentially degradable (B 2 ) and undegradable (C) fractions of NDF corrected for protein and ash, the dynamic lag rates, the degradations rates, and the specific growth rates of microorganism upon fraction B 2 were obtained, as well as the degradability coefficients and the rumen fill effect of NDF. As a result, it was possible to observe that the non-structural carbohydrates comprised a minor fraction of the total carbohydrates in the pasture samples in both seasons. The structural carb...

Kinetics of digestion of low-quality forage grazed by beef cattle fed supplements containing increasing levels of rumen undegradable protein

“…Nonetheless, the CNCPS system assumes that fraction B 2 is homogeneous and shows a single specific growth rate. Working with natural pastures, Vieira et al (2000b) found average values of 0.0357 h -1 , which was a result close to the estimates obtained in the present study.…”

“…Besides, other important quantitative variables in the feeds can be estimated, such as the energy availability and daily amount of metabolizable protein, which enables the prediction of animal performance based on known dietary inputs (Vieira et al, 2000c;Jardim et al, 2013;Jardim et al, 2015;Higgs et al, 2015). In the present study (Table 4), the average RF(I) was approximately 32% greater than RF(D), a situation that was also observed by Vieira et al (2000b) based on extrusa samples taken from a tropical grassland.…”

“…Malafaia et al (1998), working with this forage plant, and Lira et al (2006), with Urochloa decumbens in the dry season, found 230 and 199 g RD(B 2 ) kg -1 DM, which are much lower values than the average observed in the current study (290 g RD(B 2 ) kg -1 DM) for the same season of the year. However, in natural-grassland conditions, in the dry season, Vieira et al (2000b) found a higher value, 301 g kg -1 DM. However, the average observed in our experiment (348 g RD (B 2 ) kg -1 DM) was higher than the almost 230-350 g kg -1 DM observed in the literature (Malafaia et al, 1998;Vieira et al, 2000b;Lira et al, 2006).…”

“…This fraction is estimated by the Cornell system by multiplying the amount of lignin by the 2.4 constant (Chandler et al, 1980); in the literature, this value is between 2 and 3 ( Van Soest, 1994;Malafaia et al, 1998). However, Vieira et al (2000b) recommended that estimates of fraction C may be based on direct biological methods, using, for instance, in situ degradation trials, which compose the methodology relative to the fiber degradation kinetics in the current study. The greater concentration of this fraction in period three may be related to the increased proportions of stems and senescent material.…”

“…In this sense, the specific growth rate of the microorganisms on dFC was estimated according to the expressions described by Van Milgen et al (1991), R. Bras. Zootec., 45(9):563-571, 2016 Vieira et al (1997), andVieira et al (2000b). Thus, by employing the definition of Schofield et al (1994), we have:…”