Excretion of purine derivatives in cows: endogenous contribution and recovery of exogenous purine bases

Two dry cows fitted with simple cannula in the rumen and duodenum, and fed with a mixed diet (straw:barley, 50:50), were used to determine endogenous losses and response of urinary purine derivatives (PDs) to duodenally infused yeast-RNA. Duodenal flow of purine bases (PBs) was determined by a dual marker system, and 15N was infused continuously into the rumen to label microbial PBs. The isotope dilution of urinary PDs in relation to duodenal PBs confirmed the presence of an endogenous fraction (236 μmol/kg LW0.75) bigger than in sheep and lower than values estimated in cows with impaired rumen fermentation. Excretion of PDs increased linearly in response to incremental supply of PBs with an equimolar recovery of 0.84 mol/mol. However, net recovery of duodenal PBs was 0.67 for the basal diet and 0.65, 0.90, 0.79 and 0.82 for the four levels of PB infusion. It is suggested that differences in digestibility between yeast-RNA and duodenal PBs might explain differences in recovery estimations

Modelling urinary purine derivatives excretion as a tool to estimate microbial rumen outflow in alpacas ('Vicugna pacos')

Three experiments were carried out to establish a model to estimate the forestomach microbial yield based on the urinary excretion of purine derivatives (PD: allantoin, uric acid, xanthine and hypoxantine) in alpacas ('Vicugna pacos'). In Experiment 1, endogenous PD excretion was measured in two fasted adult male alpacas for seven consecutive days. Daily urinary PD excretion (μmol/kg BW0.75) decreased during fasting to a minimum value of 194.8 (s.e. 18.4), ranging from 215.3 to 174.3. In Experiment 2, the relationship between purine bases (PB) input and urinary PD output was defined in two alpacas fitted with an infusion catheter at the terminal third compartment of the forestomach (C3). Animals were fed alfalfa hay at a maintenance level, and four RNA-doses (4.2, 8.3, 12.5 and 16.6 mmol PB/day; RNA from Torula yeast) were continuously infused at random into the C3 in four successive 120 h-periods. Urinary recovery of C3 infused purines averaged 0.615 (s.e. 0.0006) mmol/day. In Experiment 3, urinary PD response to levels of feed intake corresponding to 100, 75, 50 and 20% of the previous voluntary intake was evaluated. The amount of PD excretion in urine increased linearly (r = 0.867) with digestible organic matter intake (DOMI), and the slope of the regression (16.7 mmol PD/kg DOMI) can be assumed as an index of microbial yield

Modelling urinary purine derivatives excretion as a tool to estimate microbial rumen outflow in alpacas (Vicugna pacos)

Three experiments were carried out to establish a model to estimate the forestomach microbial yield based on the urinary excretion of purine derivatives (PD: allantoin, uric acid, xanthine and hypoxantine) in alpacas (Vicugna pacos). In Experiment 1, endogenous PD excretion was measured in two fasted adult male alpacas for seven consecutive days. Daily urinary PD excretion (mu mol/kg BW0.75) decreased during fasting to a minimum value of 194.8 (s.e. 18.4), ranging from 215.3 to 174.3. In Experiment 2, the relationship between purine bases (PB) input and urinary PD output was defined in two alpacas fitted with an infusion catheter at the terminal third compartment of the forestomach (C3). Animals were fed alfalfa hay at a maintenance level, and four RNA-doses (4.2, 8.3, 12.5 and 16.6 mmol PB/day: RNA from Torula yeast) were continuously infused at random into the C3 in four successive 120 h-periods. Urinary recovery of C3 infused purines averaged 0.615 (s.e. 0.0006) mmol/day. In Experiment 3, urinary PD response to levels of feed intake corresponding to 100, 75, 50 and 20% of the previous voluntary intake was evaluated. The amount of PD excretion in urine increased linearly (r = 0.867) with digestible organic matter intake (DOMI). and the slope of the regression (16.7 mmol PD/kg DOMI) can be assumed as an index of microbial yield

A comparison of the excretion rate of endogenous purine derivatives in the urine of Bos indicus and Bos taurus steers

Estimates of microbial crude protein (MCP) production by ruminants, using a method based on the excretion of purine derivatives in urine, require an estimate of the excretion of endogenous purine derivatives (PD) by the animal. Current methods allocate a single value to all cattle. An experiment was carried out to compare the endogenous PD excretion in Bos taurus and high-content B. indicus ( hereafter, B. indicus) cattle. Five Holstein - Friesian ( B. taurus) and 5 Brahman (> 75% B. indicus) steers ( mean liveweight 326 +/- 3.0 kg) were used in a fasting study. Steers were fed a low-quality buffel grass (Cenchrus ciliaris; 59.4 g crude protein/kg dry matter) hay at estimated maintenance requirements for 19 days, after which hay intake was incrementally reduced for 2 days and the steers were fasted for 7 days. The excretion of PD in urine was measured daily for the last 6 days of the fasting period and the mean represented the daily endogenous PD excretion. Excretion of endogenous PD in the urine of B. indicus steers was less than half that of the B. taurus steers ( 190 mu mol/kg W-0.75. day v. 414 mu mol/kg W-0.75. day; combined s.e. 37.2 mu mol/kg W-0.75. day; P< 0.001). It was concluded that the use of a single value for endogenous PD excretion is inappropriate for use in MCP estimations and that subspecies-specific values would improve precision