Estimation of the Flow of Microbial Nitrogen to the Duodenum Using Urinary Uric Acid or Allantoin

Abstract

Data were collected from six experiments using duodenally cannulated Holstein dairy cows (88 combinations of cow and period) to evaluate the relationship between urinary purine metabolites and microbial N flow. Experiments evaluated the effects of dietary factors on microbial N production, which included 1) varying concentrations of ruminally degradable protein and nonstructural carbohydrates, 2) supplemental sources of protected amino acids, 3) grass silage treated with fibrolytic enzymes, 4) bacterial inoculation of corn silage, and 5) ruminal starch availability as affected by corn silages of varying maturity. The coefficient of determination for individual experiments that measured the relationship between microbial N flow and allantoin or uric acid excretion in urine ranged from 0.01 to 0.68 and 0.02 to 0.82, respectively. Across all experiments, the coefficients of determination between microbial N flow and allantoin or uric acid excretion in urine were r2 = 0.002 and 0.11, respectively. Removal of data from one experiment improved the overall coefficient of determination between microbial N flow and urinary uric acid to r2 = 0.32. Urinary allantoin excretion across experiments was negatively correlated with microbial N flow, but urinary allantoin excretion within experiments was positively correlated with microbial N flow. Uric acid excretion in urine was positively correlated with microbial N flow across and within experiments, except for one experiment. Our data demonstrate that uric acid excretion in urine can be used to predict microbial N production, except in early lactation, and that urinary allantoin excretion cannot be used to predict microbial N production accurately among cows at different stages of lactation.

Parâmetros ruminais, balanço de compostos nitrogenados e produção microbiana de vacas leiteiras alimentadas com soja e seus subprodutos

“…Segundo Johnson et al (1998), a relação ácido úrico e derivados de purina na urina pode variar com a dieta e o estado fisiológico do animal. A média nesta pesquisa usando coleta spot de urina de 39,06 mmol/dia está na faixa descrita por Valadares et al (1999), de 35,5 a 52,4 mmol/dia, obtida por coleta total de urina e de 24,6 a 52,6 mmol/dia, com amostra spot de urina.…”

Substituição do milho e do feno de capim-tifton por palma forrageira. Produção de proteína microbiana e excreção de uréia e de derivados de purina em vacas lactantes

“…Segundo Johnson et al (1998), a relação entre ácido úrico e derivados de purina na urina pode variar conforme a dieta Do mesmo modo, as excreções urinárias de alantoína não foram influenciadas pela inclusão de palma na dieta, sendo obtido valor médio de 288,42 mmol/dia, correspondente a 84,25% da excreção dos derivados totais de purina. Esse percentual foi próximo aos verificados por Vagnoni & Broderick (1997), Silva et al (2001) e Souza et al (2006), de 86,6; 71,90 a 86,10 e 82,24%, respectivamente.…”

Caroço de algodão em dietas à base de palma forrageira para vacas leiteiras: síntese de proteína microbiana

“…Portanto, esta amplitude de excreção de ácido úrico e alantoína na urina em relação aos DP fica condicionada ao estádio fisiológico do animal e aos tratamentos dietéticos (Johnson et al, 1998).…”