Harnstoff und Allantoin in der Milch von Kühen während und nach energetischer Überversorgung

Evaluation of milk allantoin excretion as an index of microbial protein supply in lactating dairy cows

The potential of milk allantoin as an index ofmicrobial protein supply was evaluated in two experiments conducted with 12 multiparous Holstein-Friesian dairy cows that examined the effects of altering the supply of metabolizable energy (ME) and fermentable metabolizable energy (FME). In the first experiment, late lactation cows received a 14·3 kg dry matter (DM) per day basal diet consisting of (g/kg DM) chopped barley straw (415), soya-bean meal (322), molassed sugar-beet pulp (197), molasses (33), urea (17) and a vitamin and mineral supplement (17) for a 21-day co-variance period. During four 16-day periods, six treatments were allocated randomly to cows, consisting of potato starch (1, 2 or 3 kg DM per day) or fat supplements (0·64, 1·27 or 1·91 kg DM per day). In the second experiment, early lactation cows received 40 kg/day (fresh weight, (FW)) of silage (307 g/kg toluene-corrected dry matter, 149 g/kg DM crude protein and 11·6 MJ/kg ME). During three 21-day periods, four treatments were evaluated consisting of supplements of either 4·1 (LI) or 8·1 (12) kg fresh weight per day of a low fat concentrate (acid hydrolysis ether extract (AHEE) 45 g/kg DM) or 3·8 (HI) or 7·5 (H2) kg fresh weight per day of a high fat concentrate (AHEE 110 g/kg DM). Both experiments showed individual cow milk allantoin concentration or excretion to be poorly correlated with urinary purine derivative excretion or calculated microbial protein supply. Use of treatment mean (TM) values dramatically improved these relationships. For pooled TM (no. = 10) values from both experiments, close relationships existed between milk allantoin excretion and concentration with milk yield (r values 0·991 and 0·883, respectively). Auto-correlation with milk yield appeared to account for milk allantoin excretion and concentration being highly correlated with urinary purine derivative excretion (r values 0·908 and 0·934, respectively) and calculated microbial protein supply (r values 0·938 and 0·945, respectively). Current experimental data indicates that measurement of milk allantoin is not a reliable indicator of microbial protein supply for individual cows.

Manometric biosensor for on-line measurement of milk urea

Performance of a prototype sensor for on-line measurement of urea in milk during milking was evaluated. The sensor was based on a manometric assay of the carbon dioxide generated by the enzymatic hydrolysis of urea. Temperature compensation of the sensor was described briefly, and was shown to be effective. The calibration of the sensor was described and resulted in a standard calibration error of about 0.15 mM of urea. The standard error of the sensor in milk was shown to be about 0.25 mM (given a physiological range of about 2-7 mM in cow milk). The sensor was simple, inexpensive, suffered from no interferences in raw milk, and completed a measurement cycle in about 5 min (less than the time to milk a typical cow). A custom made sampling device, whereby milk was passively collected from the milk line under vacuum, was shown to collect an ample volume within 10 s to run a test with the sensor. No measurable bubbles or foam were introduced from the sampling mechanism so that the milk sampled was not diminished in density compared to samples taken by other methods.

Mammary and renal excretion of purine metabolites in relation to energy intake and milk yield in dairy cows

This investigation was conducted to quantify the purine excretion of cows and to evaluate milk allantoin as an estimator of synthesis of microbial protein in the rumen. Concentrations in plasma of allantoin and uric acid and their excretion in urine and milk were determined using 16 Holstein cows at 21 to 315 d of lactation and yielding 8 to 36 kg/d of milk. The mean daily intake of a 55:45 roughage and concentrate diet was 16.3 kg of DM with 106 MJ of NEL and 13.8 to 16.0% CP. Total urine was collected over 24 h, plasma samples collected four times, and milk samples collected twice on the same day. Analyses of purine metabolites were performed with HPLC. On average, excretion of allantoin in urine and milk was about 294 and 4.1 mmol/d for allantoin and 35 and 1.1 mmol/d for uric acid. Excretion of allantoin in milk was correlated to concentration in plasma (r = .84). As milk yield increased, percentage of milk allantoin increased from .6 to 2.4% of total allantoin excretion (r = .85). The correlations of NEL intake with allantoin excretion in milk (r = .80) and in urine (r = .84) were similar. Daily milk yield was correlated with plasma allantoin (r = .78) and milk allantoin excretion (r = .95). We concluded that determination of milk allantoin is a useful, noninvasive method to monitor rumen microbial protein synthesis.