1. Association of Official Analytical Chemists, 1984. Official Methods for Analysis of the Association Official Agriculture Chemists, 14th Edition. Association Official Agriculture Chemists AOAC, Washington, DC, pp. 156–157.
2. Agriculture Research Council, 1980. The Nutrient Requirements of Ruminants. Livestock Commonwealth Agricultural Bureaux. Slough: Farnham Royal, UK.
3. Urinary excretion of allantoin and allantoin precursors by sheep after different rates of purine infusion into the duodenum;Balcells;J. Agri. Sci. Cambr.,1991
4. Beever, D.E., Siddons, R.C., 1986. Digestion and metabolism in the grazing ruminant. In: Milligan, L.P., Grovum, W.L., Dobson, A. (Eds.), Control of Digestion and Metabolism in Ruminants. Prentice Hall, Engwood Cliffts, NJ, pp. 479–497.
5. Chen, X.B., Gomes, M.J., 1995. Estimation of Microbial Protein Supply to Sheep and Cattle Based on Urinary Excretion of Purine Derivatives — An Overview of the Technical Details. Occasional Publication 1992. International Feed Resources Unit, Rowett Research Institute, Bucksburn, Aberdeen AB2 9SB, UK.