Urinary excretion of purine derivatives in Yerli Kara cattle

The urinary excretion of purine derivatives (PD) was measured in four Yerli Kara bulls in two experiments, a fasting experiment lasting for 7 days and the other , where animals were given a diet containing 30% wheat straw and 70% compounded feed at four levels of intake (40,60,80 and 95% of voluntary feed intake). In the second experiment, which was carried out according to a 4x4 Latin Square design, four animals receiving 60 and 95% levels of intake were also given a single injection of 8- ''1''4C - uric acid via a jugular catheter. In Addition to the above two experiments the activity of xanthine oxidase and uricase in plasma, liver and intestinal mucosa obtained from Yerli Kara cattle was also determined.In the first experiment,fasting PD excretion averaged 0.691 (±0.053) mmol/kgW''0''.''7''5/d. Glomerular filtration rate GFR), tubular load and net re-absorption of allantoin between pre fasting and fasting were statistically significant (P<0.05). In the second experiment the recovery of injected 8 - ''1''4C - uric acid as total PD was 72.5 and 89.9% for 60 and 95% feeding levels, respectively. The average recovery was 81%. Plasma kinetics measured by 8 - ''1''4C - uric acid indicated that the total compartment pool size was 214.0 (±43.8) and 250.3 L (±29.5) for 60 and 95% feeding levels, respectively. GFR, tubular load and net re-absorption of uric acid and allantoin were not affected by feed intake. The allantoin : PD molar ratios changed between 0.78 to 0.93 for the four levels feed intake. There were significant correlations between PD excretion (expressed as mmol/d and μmol/kg W''0''.''7''5/d) and DDMI (kg/d and kg/kg W''0''.''7''5/d) and DOMI (kg/d)(r=0.99, P<0.01). The rate of PD excretion as a linear function of feed intake was 16.4 mmol/kg W''0''.''7''5 DDMI, 19.8 mmol/kg DDMI and 22.7 mmol/kg DOMI. Xanthine oxidase and uricase activities were; 1.34 (±0.72) and .44 (±0.05) and 0.13 (±0.03) and 0.08 (±0.03) unit/g fresh tissue in liver and intestinal mucosa, respectively. In plasma xanthine oxidase activity was 5.0 (±1.2) unit/L while uricase activity was absent. It appears that the PD excretion is related to feed intake and PD excretion could be used as an index to estimate microbial protein supply as well as to measure DDMI or DOMI in Yerli Kara cattle. The endogenous excretion was estimated as 0.691 mmol/kg W''0''.''7''5/d and the average recovery of injected 8 - ''1''4C - uric acid in urine was 0.81. Hence the following model is suggested for Yerli Kara cattle in Turkey. PD excretion (Y mmol/d) = 0.81 x (PD absorption, mmol/d) + (0.691 W''0''.''7''5). (7 Tables and 21 refs. included)