Determination of oxytocin in milk of cows administered oxytocin.

To address people's concerns of exogenous oxytocin (OT) administration to lactating bovines, a study was undertaken to (a) establish an enzyme immunoassay (EIA) for OT determination in milk, (b) quantify OT in milk of cows administered OT, and (c) study influence of pasteurization on OT stability in milk. A sensitive EIA validated according to the criteria of European Union-Decision 2002/657/EC was developed for OT in skim milk in an analytical range of 10-250pgmL(-1) with a decision limit (CCalpha) of 30pgmL(-1) and detection capability (CCbeta) of 41.5pgmL(-1). Milk samples collected from cows (n=38) administered either 25 or 50IU OT prior to milking were investigated for the presence of OT. There was no significant difference among both groups with the mean concentrations of OT being 15.8 and 14.9pgmL(-1) for cows subjected to 25 and 50IU OT administration, respectively. The OT levels in skim milk of control cows (n=30; untreated) were basal (around 10pgmL(-1)). All the analyzed milk samples were below the CCalpha value of 30pgmL(-1). Pasteurization of OT spiked milk samples at different temperature and sample holding conditions reduced the immunological activity of OT to 43% at 110 degrees C. However, no further decline occurred in the immunological activity with increased pasteurization temperature and time. It was concluded that the milk OT concentrations after OT administrations were minimal and below the assay decision limit. However, OT was quite stable to pasteurization in OT spiked milk.