Estimation of microbial protein supply in ruminant animals based on renal and mammary purine metabolite excretion. A review

Abstract

The potential of mammary and renal purine metabolite excretion as a technique for the assessment of microbial protein supply in ruminant animals is reviewed. Data reported in the literature tends to support the validity of the assumptions of the technique that purines entering the duodenum are essentially microbial in origin and that following metabolism, purine catabolites (collectively allantoin, hypoxanthine, uric acid and xanthine) are quantitatively recovered in urine. The most convincing experimental evidence suggests that secretion of purine metabolites in milk is of little value for the assessment of microbial protein supply due a mumal correlation with milk yield. In contrast, use of urinary purine metabolite excretion does appear to provide estimates of microbial protein supply that, are in general, consistent with values derived using standard in vivo procedures. However, the accuracy of this approach is largely dependent on obtaining representative samples of rumen microbes and the ability to account for variations in non-renal excretion and endogenous purine losses. In conclusion, urinary purine metabolite excretion appears to represent a valid noninvasive procedure to assess relative differences, rather than quantitative estimates of microbial protein supply in ruminant animals.

Effect of supplemental energy source and frequency on growing calf performance1

“…Samples were cooled on ice, transported to the laboratory, and frozen until analysis. Purine derivative-to-creatinine ratio (PD:CR) was used as an indicator of relative changes in rumen microbial flows to the intestinal tract (Valadares et al, 1999;Shingfield, 2000;Whittet et al, 2004). Creatinine and purine derivatives were determined using HPLC (Waters Corp., Milford, MA) according to the procedure of Shingfield and Offer (1999).…”

“…Therefore, PD:CR in spot urine samples can be used to estimate microbial production. Shingfield (2000) concluded that with current understanding, purine degradation products may be used to determine relative differences in microbial production -absolute values will require more research. We are therefore reporting PD:CR as an indicator of treatment effects on microbial production.…”

Microbial protein synthesis in young steers fed with grass silage and extruded corn

“…The conversion of degradable protein into MP in the rumen requires the contribution of energy for ruminal microorganisms (Beever and Cottrill, 1994;Firkins et al, 2007). Microbial protein production is generally considered proportional to the energy available for fermentation in the absence of acidosis; however, the efficiency of microbial protein synthesis (EMPS) is affected by other factors, including those that emphasize feeding level and ruminal synchrony (Dewhurst et al, 2000;Shingfield, 2000). The use of diets with a high nonstructural carbohydrate content increases passage rate, the supply of metabolizable energy and intestinal digestible protein, and EMPS (Firkins et al, 2006).…”

“…Some of these are based on measurements of digesta flow, which requires fistulated animals and microbial markers, thereby rendering these methods questionable from the point of the animal's well-being (Shingfield, 2000;González-Ronquillo et al, 2004). There are also discrepancies between estimations of microbial N flow towards the duodenum with the use of different markers (Shingfield, 2000). The estimation of MPS from purine derivatives (PD) in the urinary excretion is a simple and non-invasive method that needs only the quantitative collection of urine.…”

Influence of Distillers Dried Grain Supplementation Frequency on Forage Digestibility and Growth Performance of Beef Cattle

“…Theoretically, purine derivative:creatinine ratios are indicative of microbial growth in the rumen (Shingfield, 2000), and if fat content of the diet was the reason for decreased BW gain in the infrequently supplemented treatment, a decreased purine derivative:creatinine ratio would be expected. Purine derivative:creatinine ratio may not be an accurate determinant of absolute quantities of microbial purine production, but has been shown to be useful in determining relative differences in purine production among treatments (Shingfield, 2000). The ratio of purine derivatives:creatinine was not different (P = 0.12) between treatments in this experiment.…”