Effects of sample handling temperatures on bovine skim milk progesterone concentrations

The effect of incubation of whole milk at various temperatures and times on the amount of progesterone (nmol/l) in the skim milk fraction was determined. For this study, milk samples were obtained from 10 pregnant Holstein cows. The whole milk samples were incubated at 37 degrees C (near normal body temperature of the cow) for 4 h and the initial skim milk progesterone concentration was determined. After that, the experiment was carried out in two main steps: (I) The test tubes containing the whole milk were divided into 4 groups and incubated at different temperatures (0, 4, 20 and 37 degrees C). Samples were removed at 30, 60, 90 and 120 min. (II) After 120 min of incubation at different temperatures, the remaining test tubes were returned to the water bath at 37 degrees C for another 30, 60 and 90 min. The initial average of skim milk progesterone concentrations after incubating the whole milk at 37 degrees C for 4 h was 11.0 +/- 4.4 nmol/l. When the whole milk was incubated at 0 degrees C, the skim milk progesterone concentration increased (P < 0.05) to 14.6 nmol/l at 30 min and reached 16.2 nmol/l at 60 min of incubation. At 4 degrees C incubation temperature, skim milk progesterone increased significantly (P < 0.05) to 15.3 nmol/l and reached 16.9 nmol/l after 90 min. When the whole milk was left at 20 degrees C, the initial skim milk progesterone values decreased to 9.5 nmol/l after 30 min incubation and no further decreases were found even if the whole milk was returned to 37 degrees C for 90 min.(ABSTRACT TRUNCATED AT 250 WORDS)