Evaluation of purine metabolites - creatinine index to predict the rumen microbial protein synthesis from urinary spot samples in Barbari goats

The study evaluated the potential of the concentration of purine metabolites (PM) in spot urine as an alternative to performing a total urine collection to predict the microbial nitrogen (MN) supply in goats. The study was conducted in two phases. Phase I was comprised of fasting metabolism trial of eight goat bucks (19.70±0.59 kg mean body weight) to quantify the contribution of basal PM excretion. PM excretion decreased (P<0.05) with feed restriction and the mean value (μmol/kgW^0.75/d) observed during fasting was 250.09±5.11. Phase II examined the response of PM excretion to feed intake and evaluated the usefulness of purine metabolites: creatinine (PMC) index in spot urine samples for prediction of rumen MN supply. The concentration of PM in total urine and spot urine was quantified in eight goat bucks (20.24±0.74 kg mean body weight) allocated in two sets of 4×4 Latin square design at four fixed levels of feed intake (95, 80, 60 and 40% of voluntary feed intake) on diet based on wheat straw and concentrate mixture (50:50). Total PM excretion increased linearly with level of intake. Urinary excretion of creatinine did not differ among groups, while the PMC index calculated from total urine and spot urine increased (P<0.05) with level of feed intake. PMC index of spot urine differentiated the feeding levels at 6 and 12 h post feeding. The relationship between PMC index in the spot urine samples collected 12 h after the morning feed and the daily total PM excretion was the highest (R²=0.82). The results confirm that PMC index in spot urine samples can serve as a potential tool for the quantification of MN supply in goats.