The Urinary Excretion of Purine Derivatives in Sheep Offered Nitrogen and Phosphorus Deficient Diets

Urinary allantoin excretion as a measure of microbial protein production, has been shown to be responsive to ruminal nitrogen (N) supply (Balcells et al. 1993). Dietary phosphorus (P) deficiency has also been observed to reduce microbial protein flow (Gunn and Ternouth 1994). The aim of this experiment was to examine the effects of P and N deficiencies upon microbial protein formation, as determined by urinary purine derivative (PD) analysis. Twenty-four cross-bred lambs (17-35 kg) were randomly allotted to 6 treatments for 10 weeks. The control was offered a high (H)P-HN diet ad libitzrrn, and 3 further groups were offered diets; low (L)PHN, HP-LN and LP-LN ad lihitcrn~. Two additional groups of lambs were pair-fed with the LP-HN and HP-LN lambs on diet HP-HN. The basal (LP-LN) diet contained chaffed barley straw fed ad libitwn, and 180-300 g of supplement consisting of sugar, gluten and mineral-vitamin mix (0.86:O. 1:0.04 ratio) depending on the liveweight (LW) of the animal. The basal diet contained 0.23 g P/kg dry matter (DM) and 13 a0 N/kg DM. Monosodium phosphate and urea were added to achieve the H dietary levels of 2.3 g P/kg DM and 20 g N/kg DM. Food intake was measured over the last 7 days and urine samples collected over the last day of the feeding period when most of the lambs offered both the LP diets had reduced their food intakes. Samples were analvsed for PDs using high performance liquid , chromatography (Balcells et al. 1992). The urinary excretion of allantoin and total PD excretion were reduced in lambs offered either the P or N deficient diets, although this effect was only significant when lambs were N deplete (LP-LN and HP-LN). Uric acid, hypoxanthine and xanthine excretion (mg/kg LW0a7?day) were not altered. The . restriction of food intake resulted in a non-significant increase in the daily excretion of PDs (126 and 100 ‘;( mg allantoin, and 152 and 135 mg total PD/kg LW 0.75 for the lambs pair-fed diets LP-HN and HP-LN respectively). The results strongly su,, oc’est that feeding either N or P deficient diets results in a reduction in microbial protein production. It is hypothesised that the effect of a P deficiency is to cause a secondary reduction of the supply of microbial protein to the animal. Is, Q+r -3744 Table 1. Intakes and urinary excretion of purine derivatives (PD) in lambs fed ad libitum high (H) or low (L) intakes of nitrogen (N) and phosphorus (P)