Test strips are coated with special chemicals that react with ammonia. The 2- to 3-centimeter strip is first slightly moistened (eg with a few drops of calf whisker) and then placed at the height of the calves' head. It is important to measure in the calves' resting area and not near the feed fence. The result is available after about 15 seconds. A value greater than 4 to 5 ppm should be viewed critically.
Test strips used – this is how they work:
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