Urinary Purine Derivatives as Index for Estimation of Ruminal Microbial Nitrogen Production in Sheep and Goats

Microbial-N production in the rumen can be estimated by using urinary purine derivatives (PD) as an index. A series of experiments were conducted to establish the relationship between urinary PD (allantoin, uric acid, xanthine and hypoxanthine) and feed intake, endogenous PD excretion and recovery rate of plasma PD in sheep and goats. Studies on factors affecting PD excretion; xanthine oxidase and uricase activities of the plasma, liver and intestinal mucosa cells; uric acid kinetic; and purine-N:total-N ratio of rumen microbes were also conducted. Male Poll Dorset Cross sheep and male Ferral goats were used. The animals were fed a diet consisting of 40% oil palm frond and 60% concentrate (OPFC). Four sheep (40.232.8kg) and four goats (39.6f1.8 kg) were used to measure urinary PD excretion at 40%, 60%, 80% and 95% of voluntary intake (VI). The proportion of plasma PD excreted in the urine was determined by using ['4~]-uric acid as a marker at 40% and 80 % of VI. Endogenous PD excretion was determined by fasting in six sheep (55.4f5.1 kg) and six goats (40.2f4.6kg). The results showed that sheep excreted significantly (p<0.05) higher PD and creatinine than goats when compared at the same level of feed intake. However, the coefficient of the relationship between PD and DOMI in goats (12.57 mmollkg DOMI) was similar to that in sheep (12.49 mmolkg DOMI). The proportion of allantoin to total PD in goats (86%) was higher than that in sheep (60%). The distribution pattern of enzymes (xanthine oxidase and uricase) activities in the plasma, liver and intestinal mucosal cells were similar in both animal species, but uricase activity of the intestinal mucosa cells in sheep was significantly higher (p<0.05) than in goats. The average daily urinary endogenous PD excretion obtained by the fasting trial for sheep (201f35 p r n o l k g7~5d - 1 ) was similar to that for goats (202f17 p o l k g W075d-1). The average percentage of total recovery of plasma PD excreted in the urine determined by using [14~]-urica cid in sheep (77f2.8 %) was not significantly different from that in goats (83f2.0 %). In the uric acid kinetics study, total tracer recovered reached a peak value of about 74.2% at 12 h for goats, and 74.4% at 15 h for sheep. The conversion efficiency of [14c]-uric acid to allantoin in the plasma pool was higher (p<0.05) in goats than in sheep, with a peak value of 40% recovery at 12 h post injection for goats and 33.5% at 15 h post injection for sheep. By 15 h, no [14~]-uriacc id was detected in the urine of both animal species. The rates of [I4c]-allantoin and [I4c]-uric acid excretions in the urine of sheep (3 1.0 and 88.0% h", respectively) were significantly (p<0.05) faster than those of goats (19.0 and 64.7% h-I, respectively), but the rates of total [I4c]- tracer were not significantly different between the two animal species (42.5% h-' and 30.3% h-I for sheep and goats, respectively). The primary compartment size in the plasma (V]) was significantly (p<0.05) larger in sheep (24.4 f3.01 mg C) than in goats (17.5k1.28 mg C) and the secondary compartment size in the tissue (Vz) of sheep was also larger (129f21.6 mg C) than that of goats (65.7f23.7 mg C). The volume of distribution (L) was 45% higher in sheep (0.898 L) than in goats (0.490 L). However, the net flux tended to be higher in goats (20.3k3.82 mg C) than in sheep (16.1A2.0 mg C). Hence, the results indicated that differences exist between sheep and goats in uric acidallantoin kinetics. The equations established for sheep and goats based on the recovery of labeled PD ['4~]-urica cid and endogenous PD excretion to determine the absorption of purines (X mmoWd) estimated from PD excretion in the urine (Y mmol/d) for sheep was Y=0.77X+0.201 X B75e~u.20 Xan d for goats Y= 0 . 8 3 ~ + 0 . 2 0 2 x ~ ~ T~h~e epu~rin. e~-N~:to~ta.l- N ratios of mixed rumen liquid-associated bacteria and solid-associated bacteria for sheep were 11.2 and 10.4, and those for goats were 8.5 and 10.0, respectively. The proposed equations to ,estb-ate rumen microbial-N production based on PD excretion was 0.753X for sheep and 0.992X for goats.

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