Response of urinary purine derivatives excretion to different levels of ruminal glucose infusion in heifers

Abstract

This study investigated the response of urinary purine derivatives (PD) excretion to increasing levels of intraruminal glucose infusion to evaluate how well this indicator reflects induced changes in microbial crude protein flow. Four rumen-cannulated heifers (482 ± 25 kg body weight) were fed at maintenance energy level with a basal diet (on fresh matter basis) of 4 kg/d hay, 1.5 kg/d concentrate and 60 g/d minerals in two equal meals. The trial comprised a control period (Control I) without glucose infusion followed by four consecutive periods in which all animals received 125 g, 250 g, 500 g or 1000 g/d of glucose, respectively. For this, daily dosages of glucose and urea (90 g/d during all periods) were divided into three portions that were dissolved in water and directly administered into the rumen during morning and afternoon feedings and once during noon. After the highest glucose dosage, a second control period was carried out (Control II). Urinary PD excretion increased with glucose infusion of 125 g/d (71.4 mmol/d) and 1000 g/d (74.2 mmol/d) over the level at Control I (53.9 mmol/d (standard error of the mean (SEM) 3.4; p = 0.012). After withdrawing glucose infusion, PD excretion (79.0 mmol/d) did not return to Control I level (p = 0.001). In contrast, faecal nitrogen (N) excretions linearly increased with incremental glucose infusion (p < 0.001) from 33.9 g/d at Control I to 39.7 g/d (SEM 0.5) at 1000 g/d of glucose and were similar in Control I and II (p = 0.086). The contradicting responses in the excretions of faecal N and urinary PD to increasing glucose infusions highlight the limited accuracy of the PD excretion as a non-invasive indicator when incremental dosages of rapidly fermentable carbohydrates are supplied.

Graded supplementation of chestnut tannins to dairy cows fed protein-rich spring pasture: effects on indicators of protein utilization

“…The total urine N was determined with a Kjeldahl apparatus (Büchi B324, Büchi Labortechnik GmbH, Essen, Germany) after digestion with the Gerhardt KT20 (C. Gerhardt GmbH & Co, Königswinter, Germany). Allantoin, uric acid and creatinine (CR) were determined by high-performance reversed-phase liquid chromatography following Dickhoefer et al (2015). The sum of allantoin and uric acid was considered to reflect total purine derivatives (PD).…”

Effects of Type of Concentrate and Timing of Supplementation on Feed Intake, Nitrogen Use, and Performance in Lactating Dairy Cows Grazing an Alfalfa-Ryegrass Sward

“…For incorporation of available N in the rumen into microbial protein, energy must be available for microbial growth. The supplementation of non-structural carbohydrates as an energy source increases rumen microbial growth and activity and thereby enhances the N incorporation into microbial protein, which, in turn, improves amino acid supply to their host and may enhance overall N use efficiency in lactating dairy cows [7,8]. However, the effects on rumen fermentation and MPS, as well as on animal performance, depend on the amount of supplement, its nutritional composition, and the extent and rate of ruminal starch degradation [9,10].…”