Avaliação de métodos para análise de nitrogênio amoniacal em fluido ruminal e de óxido crômico em amostras de fezes de bovinos / Evaluation of methods for analyses of ammonia nitrogen in rumen fluid and chromium in cattle feces

AUTOR(ES)
FONTE

IBICT - Instituto Brasileiro de Informação em Ciência e Tecnologia

DATA DE PUBLICAÇÃO

15/02/2012

RESUMO

This dissertation was based on two different experiments. The first one was conducted to evaluate the accuracy of two different methods in measuring the ammonia nitrogen (N-NH3) concentration in rumen fluid: a catalyzed indophenol colorimetric reaction (CICR) and the Kjeldahl distillation (KD). Five buffered standard solutions containing volatile fatty acids, true protein, and known ammonia concentrations (0, 3, 6, 12, and 24 N-NH3 mg/dL) were used to simulate rumen fluid. Different ratios (10:1, 7.5:1, 5:1, 2.5:1, 1:1, 1:2.5, 1:5, 1:7.5, and 1:10) of a potassium hydroxide solution (KOH, 2 mol/L) to standard solutions were evaluated by the KD method. The accuracy of each method was evaluated by adjusting a simple linear regression model of the estimated N-NH3 concentrations on the N-NH3 concentrations in the standard solutions. When the KD method was used, N-NH3 was observed to be released from the deamination of true protein (P<0.05), and an incomplete recovery of N-NH3 was observed (P<0.05), except for 7.5:1 and 5:1 ratios of KOH solution to standard solutions (P>0.05). The estimates of the N-NH3 concentration obtained by the CICR method were found to be accurate (P>0.05). After the accuracy evaluation, ninety-three samples of rumen fluid were evaluated by the CICR and KD methods (using the 5:1 ratio of KOH solution to rumen fluid sample), assuming that the CICR estimates would be accurate. The N-NH3 concentrations obtained by the two methods were different (P<0.05) but strongly correlated (r = 0.9701). Thus, it was conclude that the estimates obtained by the Kjeldahl distillation using a 5:1 ratio of KOH solution to rumen fluid sample can be adjusted to avoid biases. Furthermore, a model to adjust the N-NH3 concentrations is suggested. In the second experiment, the objective was to evaluate combinations between acid digestion techniques and spectrophotometric quantification to measure chromium concentration in cattle feces. It was evaluated digestion techniques based on the use of nitric and perchloric acids, sulfuric and perchloric acids, and phosphoric acid. The chromium quantification in the solutions was performed by colorimetry and by atomic absorption spectrophotometry (AAS). When AAS was used, it was also evaluated the addition of calcium chloride to the solutions as releasing agent. Several standard samples containing known chromium contents were produced (0, 2, 4, 6, 8 and 10 g of chromium per kg of feces) using cattle feces obtained from three different animals to evaluate the accuracy of the different combinations of techniques. The accuracy was evaluated by adjusting a simple linear regression model of the estimated values on the actual values of chromium in the standard samples. Independently on digestion technique, the estimates of chromium contents in the standards samples obtained by colorimetry were not accurate (P<0.05). Considering the AAS quantification, the digestion techniques based on nitric and perchloric acids and based on sulfuric and perchloric acids provided complete chromium recovery (P>0.05). The use of digestion technique in phosphoric acid provided incomplete recovery of the fecal chromium (P<0.05). Subsequently, the digestion techniques in nitric and perchloric acids and digestion in sulfuric and perchloric acids, both evaluated by AAS, were compared using 84 cattle feces samples. The results indicate that these techniques provide similar contents (P>0.05) of fecal chromium.

ASSUNTO(S)

nitrogênio amoniacal cromo nutrição de gado nutricao e alimentacao animal ammonia nitrogen chromium cattle nutrition

ACESSO AO ARTIGO

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