Does an outdoor pen have beneficial effects in calves?

The efficacy of 0.2 % formic acid, 0.3% and 0.6% propionic acid and 0.05 % H2O2 against yeast growth in whey was tested in the laboratory. After inoculation with cultures of naturally contaminated whey and the addition of the preservatives the whey samples were incubated during four days. Gas pressure was measured continuously. Yeast numbers were counted once a day. The samples containing formic acid had the lowest yeast count and the smallest fluctuations in pressure (P < 0.05). Thus formic acid proved to be the most efficient whey preservative. H2O2 suppressed yeasts more efficiently than did propionic acid during the first two days but had no lasting effect, presumably because H2O2 had been used up. Although the yeast count was not reduced in the samples containing propionic acid gas pressure frequently decreased below 0, indicating that gas was used by microbes. Simple on farm tests, which measure gas formation semiquantitatively as an indicator for the presence of yeasts may therefore yield false negative results when propionic acid is used as a preservative.