Contribution of dietary nitrogen and purine bases to the duodenal digesta: comparison of duodenal and polyester-bag measurements

Abstract

Four ewes fitted with ruminal and duodenal T-piece cannulas were given four diets in a 4 X 4 factorial design. Diets consisted of 700 (HF) or 400 (LF) g/day of ammonia-treated barley straw supplemented respectively with 150 or 600 g/day of concentrate made up with barley plus either soya-bean meal (SBM) or fish meal (FM) as the protein source, offered at 2-h intervals. Duodenal flows of digesta were estimated by the dual-phase technique using Co-EDTA and Yb-acetate as markers and ( 15 NH 4 ) 2 SO 4 was infused into the rumen to label microbial N. Bacteria were isolated from the liquid (LAB) or solid (SAB) rumen digesta. Purine bases (PB) were isolated by precipitation in an acid solution ofAgN0 3 , and microbial contribution either to the duodenal nitrogen (N) or PB were determined by 15 N measurements in duodenal digesta and bacteria. Simultaneously, the rumen degradation of N and PB contained in SBM and FM was studied by incubating supplements in polyester bags in the rumen. PB content (jimol/g dry matter) and guanine: adenine (G/A) ratio of barley straw was barley grain, SBM, and FM, respectively. Duodenal flow ofPB (mmol/day) was significantly higher than PB intake on all diets and G/A ratio showed a mean value of 0-97, similar to the ratios determined in SAB (0-80) and LAB (1-04) and much lower than diets (1-31 to 4-32). Microbial contribution to duodenal N flow ranged from 43-3% to 61-0%, being higher in SBM (59-0%) than in FM (46-7%) diets. However, microbial contribution to duodenal PB was not affected by the experimental treatment, accounting for proportionately 0-77 of total PB at the duodenum. Rumen degradability of PB was much higher than that of total N and in both cases degradability was higher in SBM than FM. Direct measurements of non-microbial N were significantly higher than values determined by the polyester-bag measurements. However, once corrected for the endogenous N (52 mgN per kg live weight) contribution, results showed an acceptable agreement. Duodenal flow of PB non-attributable to microbes (unlabelled PB) showed a mean value of 3-25 mmol/day without a significant effect of dietary treatment. However, undegradable PB supply determined for 0-02, 0-05 and 0-08 per h fractional outflow rates were proportionately lower than 0-025 with SBM and 0-100 with FM diets of the estimated duodenal PB flow. Despite the magnitude of the unlabelled duodenal PB, the close agreement between G/A ratios in duodenal digesta and bacteria suggests that the contribution of dietary PB to the duodenal flow was low and seems to confirm the reliability of values obtained from polyester-bag measurements.

Comparison of purines and nitrogen-15 as microbial flow markers in beef heifers fed barley- or corn-based diets

“…but consistent with the results reported by Perez et al (1997), there were large differences between the 15 N-enrichment of duodenal total N and duodenal purine N. This is an indication that duodenal purines are predominantly of microbial origin and reflects the relatively greater ruminal degradability of feed purines compared to the degradability of total feed N. Perez et al (1997) found a significant contribution (from 13 to 27% in whole digesta and from 2 to 17% in solid digesta) of feed purines to the duodenal purine flow in sheep and suggested that feed purines flow mainly with liquid duodenal digesta. Our data show feed purine contribution (based on 15 N-enrichment data) to duodenal liquid digesta purines of 3.5% (averaged between the two diets) and to duodenal solid digesta purines of 19.7%.…”

“…The contribution to whole digesta purines was on average 9.1%. However, unlike results by Perez et al (1997), microbial purines comprised on average 96.5% of the liquid digesta purines. Work using real-time PCR has shown that DNA released as a result of plant cell lysis into duodenal contents is degraded almost instantaneously (Alexander et al 2004).…”

“…Perez et al (1996) reported comparable results with the current study; greater (by 20% on average) MCP flow in sheep when 15 N was used as a microbial marker compared with purines. In a series of metabolism trials, Perez et al (1997, 1998a), Orellana Boero et al (2001, Gonzalez-Ronquillo et al (2003), and Vicente et al (2004) used continuous intraruminal infusion of 15 N to label bacterial purines and consequently urinary PD and to estimate feed purine contamination of duodenal purines and endogenous PD excreted by sheep and cattle. With sheep, Perez et al (1997) reported greater proportions of MN in duodenal digesta when 15 N was used as a microbial marker compared with purines, with differences between the methods ranging from 3 to 26% (using liquidassociated bacteria as a reference).…”

“…The ratio of purine N to total N in ruminal bacteria was determined in the experiment (see Marker Infusion and Sampling for details on isolation of ruminal bacteria). The contribution of bacterial purine N to duodenal purine N in LDD, SDD, or WDD and to urinary PD was found as: (steadystate 15 N-enrichment of duodenal purine or urinary PD N, APE) ÷ (steady-state 15 N-enrichment of bacterial purine N, APE) (see also Perez et al 1997;Perez et al 1998a;Orellana Boero et al 2001;Gonzalez-Ronquillo et al 2003). The proportion of bacterial N originating from ruminal ammonia N was found as: (steady-state 15 N-enrichment of bacterial N, APE) ÷ (steady-state 15 N-enrichment of ammonia N, APE).…”

“…The use of nucleic acids or purine bases (PB) for assessing MCP flow in ruminants is based on the assumption that dietary purines are rapidly and extensively degraded in the rumen (Smith and McAllan 1970;McAllan and Smith 1973) and that the purine:N ratio is much smaller in feed than in ruminal microbes. However, Perez et al (1997) reported that dietary purines accounted for 13 to 27% of the total purine flow at the duodenum of sheep. Vicente et al (2004) found an even greater (33%) flow of feed purines to the duodenum of cattle fed high-concentrate diets.…”