Fração endógena e recuperação urinária de derivados de purinas obtidas por diferentes métodos em bovinos nelore / Endogenous fraction and urinary recovery of purine derivatives obtained through different methods in Nelore cattle

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

Two experiments were executed utilizing eight Nelore heifers. The first experiment had the following objectives: aimed to evaluate the endogenous fraction at urinary excretion of purine derivatives (DP) in Nelore cattle fed single diet offering different levels of dry matter (MS); to establish the proportion of purines into abomasum recovered from urine and; to verify the effect of the level of intake upon microbial production (Nmic). Heifers were accomodated in individual stalls, with average weight of 258 20kg, fistulated at rumen and abomasum, being four of those also fistulated at the ileum. The experimental design was 2 balanced latin squares 4 x 4. Treatments constituted of four levels of MS offer: 1.2, 1.6, 2.0 and 2.4 % of live weight (PV). The experiment was conducted in four periods of 14 days, being the first 7 days for adaptation. Endogenous losses and recovery of purine bases as purine derivatives were estimated by regression between daily excretion of purine derivatives in urine (Y) and purine bases into the abomasum (X), expressed in mmol/kg0.75, represented respectively by the intercept and the regression coefficient. Endogenous losses were also evaluated by the regression between DP excretion, in mmol/kg 0.75, and the intake of MS, in g/kg0.75. Despite variation limits of MS intake obtained were 1.16 and 1.84% of live weight (PV), the maximum value of 2.4% of PV was not achieved. Total apparent digestibility coefficient of MS and MO varied linearly (P >0.05) with levels of MS offer in diet, with reduction of 2.17 % and 2.21 % to each 1% of live weight respectively. Apparent digestibility coefficient of RNA at small intestine (ID) was not affected (P >0.05) by the levels of MS offered in diet, obtaining an average value of 75.63%. True digestibility of 92.78% (P >0.0001), was obtained by the regression between the amount of absorbed RNA (Ŷ) as a function of RNA flux into abomasum (X), expressed in mmol/kg0.75. The mean relation of N-RNA:N- total in isolated ruminal bacteria was 0.1369. Daily flux of RNA (RNA Abo) and microbial production (Nmic Abo) into abomasum as a function of the level of MS offer in diet presented a quadratic behavior, and estimated maximum values of 1.50 mmol/kg0.75 and 55.20 g Nmic respectively to the levels of MS offer 2.43 and 2.45% of PV. Daily urinary excretion of DP, in mmol/kg0.75, increased linearly (P >0.05) with the level of MS offer in diet. And when it was related to the observed intake of digestible MO, (kg/day), the excretion (P >0.0001) of 34.415 mmol of DP to each kg of digestible MO ingested was verified. When the excretion of purine derivatives, expressed in mmol/day, was related to the intake of NDT, kg/day, it was observed that there were excretion (P >0.0001) of 32.15 mmol to each kg of NDT consumed. Considering the intake of MS expressed in g/kg0.75 and the excretion of DP in mmol/kg0.75, a regression was obtained (P >0.0001): Ŷ= 0.0196x + 0.2421, where 0.2421 mmol/kg0.75 or 0.24 mmol/kg0.75, represents the endogenous excretion of DP. Daily excretion of purine derivatives, mmol/kg0.75, as a function of RNA flux into abomasum, mmol/kg0.75, was adjusted to regression (P >0.0001) Ŷ = 0.8601x + 0.4603 (R2 = 0.661), where 0,86 represents the recovery of purines as derivatives in urine and the value of 0.4603 mmol/kg0.75 represents the endogenous fraction. Microbial production estimated by purine derivatives in urine, expressed in g N/day, as a function of the levels of MS offer in diet, presented linear regression (P >0.05), estimating increases of 22.80 g Nmic per 1 % of the MS offered. It was concluded that: different methods resulted in estimates of 0.46 mmol/kg0.75 and 0,24 mmol/kg0.75 to endogenous excretion of purine derivatives in Nelore cattle; the recovery of absorbed purines as derivatives in urine was of 0,86 and the real digestibility of RNA in ID, 0.93, is greater than the value assumed in literature for microbial production calculation. In the second experiment, the objective was to estimate the endogenous contribution in urinary excretion of purine derivatives in Nelore cattle by means of different levels of RNA infusion into abomasum. It was used eight heifers of Nelore breed, with average weight of 296 15 kg, fistulated at rumen and abomasum, accomodated in individual stalls. The experimental design was 2 balanced latin squares 4 x 4, with four animals, four treatments and four experimental periods. Treatments constituted of infusions of RNA into abomasum at dosages of 0, 33, 66 and 100 mmol/day. Every animal received a diet balanced with levels close of their maintenance levels during seven days aiming the adaptation, before beginning of infusions. Following the adaptation to the diet, four experimental periods of nine days each ensued according the scheme: from 1st to 5th day samples of digesta from the abomasum were collected; from 1st to 4th day total collection of urine and feces; from 5th to 9th day infusion of RNA into abomasum; from 6th to 9th day total collection of urine; at the 9th day of the fourth period samples of digesta from the rumen were collected. Therefore, before executing the infusion in each animal, fluxes of microbial protein into abomasum were obtained using purine bases and urinary excretion of purine derivatives. Hence, the flux of purine bases into abomasum was obtained summing up the values of each animal before the infusion with respective infusion quantity. Flux of N total into abomasum, N-RNA and RNA before infusions were, in average, 51.15 g/day; 5.11 and 35.23 g/day, respectively. Daily excretion of purine derivatives (Ŷ) mmol/kg0.75, as a function of RNA flux into abomasum (X), mmol/kg0.75, was adjusted to the regression (P >0.0001): Ŷ = 0.30127 + 0.74143 X, indicating that 0.30 mmol/kg0.75 correspond to endogenous losses and 0,74 is the purine recovery absorbed in the abomasum as purine derivatives in urine.

ASSUNTO(S)

produção microbiana bases purinas purine bases rumen ruminantes reproducao animal microbial production

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