Abstract :
This study aimed to investigate the relationship between microbial N (MN) yield and urinary
excretion of purine derivatives (PD) from the rumen in Dorper × thin-tailed Han crossbred
sheep. Twelve Dorper × thin-tailed Han crossbred, non-castrated male lambs (41.3 ± 2.8 kg
body weight) fitted with ruminal and duodenal cannulae were randomly assigned to one
of three levels of DM intake: ad libitum intake, 70%, or 50% of the ad libitum intake, with
four lambs at each level. The MN yield from the rumen was measured using 15N or purine
bases (PB) as a microbial marker, and urinary PD were determined by colorimetric methods.
Microbial components (OM, N, PB and ratio of PB to N) were not affected (P > 0.05) by dietary
treatment. The MN yield measured using PB was slightly lesser and more variable than using
15N. No difference in MN yield was found between markers. The efficiency of MN synthesis
(g N/kg organic matter apparently digested in the rumen) was not affected (P > 0.05)
by feed intake regardless of the marker used. Urinary PD decreased significantly (P < 0.05)
with decreasing level of feed intake and the molar recovery of duodenal PB measured with
digesta markers as urinary PD was 0.83 (r2 = 0.89, P < 0.001). Urinary PD excretion was linearly
correlated with DOMI (r2 = 0.94, P < 0.001), and MN yield estimated by using either
15N or PB (r2 = 0.91 and 0.80, respectively, P < 0.001). These results suggest that urinary PD
excretion is an accurate indicator of MN synthesized in the rumen, and an equation, MN
(g/d) = 0.030 + 0.741 × PD (mmol/d), is proposed to predict the MN yield from the rumen of
Chinese sheep.
