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.

Keywords:

• allantoin
• cattle
• feeding
• glucose
• microbial protein
• ruminant

Acknowledgements

We are grateful to Mrs M. Paschke-Beese, Mrs A. Hollmann and Mrs M. Gosse for their assistance during laboratory analyses. Furthermore, we thank Mrs N. Selje-Aßmann and Mr P. Lawrence for English revision and valuable comments.

Notes

1. Theoretical basis of the calculation of urinary PD excretion: (1) Efficiency of MCP synthesis = 10.1 g MCP/MJ ME intake (GfE 2001); (2) Proportion of N in purines = 0.116 g/g of microbial N; (3) Praecaecal digestibility of MCP = 0.83; (4) Renal clearance rate of absorbed PD = 0.85; (4) Endogenous PD excretion in cattle = 0.385 mmol/kg^0.75 BW (Chen and Ørskov 2003).

Additional information

Funding

This study was conducted within the research project “Food Chain Plus” funded by the German Federal Ministry of Education and Research [project number 0315538A; 2010–2015].