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Procedure for total urine collection
The objective is to collect all the urine produced by the animal. Good separation of urine from faeces is essential. This may require the use of metabolism cages/stalls or urine collection harness.
The collection can be made as a bulk for the whole period. However, where analysis facility allows, it is better to make the urine collection daily. Daily collections provide us with additional information on the variability of the daily measurement. From our experience, this day-to-day variation is usually about 10%.
Urine is collected in a container with approximately 100 ml of 10% H2SO4. The final pH of urine should be below 3. It is essential to acidify the urine to prevent bacterial destruction of PD in urine. It may be necessary to check the pH on the first day of collection and make necessary adjustment of the amount of acid used accordingly. Slight excess of acid will not affect the analyses.
PD concentration in undiluted urine (straight from the animal) is very high and precipitation (particularly of uric acid) can occur during storage. This makes difficult to take a representative sample of urine for analysis. Dilution by 3 - 4 times prevents the occurrence of precipitation. Consider diluting the urine just after collection (i.e. before storage) as follows:
| 1 |
Record the original weight of the urine. The daily urine output may vary with individual animals and diets, 0.5-2 Land 20-30 L for sheep and cattle, respectively. Add tap water to a constant final weight (4 kg for sheep, 50 kg or even higher for cattle *). So the final volume of diluted urine is the same for all animals and every day. The advantages are: (a) it is easy to bulk the daily samples if needed (just by taking an equal volume of all daily samples); (b) it is easy for the analysis since all samples can be further diluted by a same factor. * If it is difficult to handle large quantity of liquid, collect a representative sample of urine and dilute it by a known factor (4-5 times). |
| 2 | Mix the diluted urine thoroughly, filter some urine through glass wool or surgical gauze, take a sub-sample of about 20 ml and store it in labeled (e.g. animal ID, feed treatment, date and time of sample collection) bottle at -20 °C. |
| 3 | Twenty ml of the diluted urine is sufficient for purine analysis, but take enough for other analyses. For example, for the determination of N in the diluted urine, it is necessary to increase the sample size accordingly. |
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