Effect of oxytocin injection to milching buffaloes on its content & stability in milk

BACKGROUND & OBJECTIVES Oxytocin (OT) injections to milch cattle for milk letdown have become a common practice amongst dairy farmers in India. Although there is no reported evidence, it is widely presumed that long term consumption of such milk leads to adverse health consequences. However, there is no information on the effect of exogenous OT injections on milk OT content and its stability during heating and gastrointestinal digestion. This study was carried out to determine the OT content in milk samples given by buffaloes with and without OT injections and to assess the stability of OT in the milk. METHODS Milk samples from milch buffaloes (Murrah buffalo) were collected from local farmers with (n=121) or without (n=120) exogenous OT injections during 3 to 5 months of lactation period. The OT content of milk samples was estimated by competitive enzyme immunoassay (EIA). The thermal and digestive stability of OT was assessed by in silico and in vitro digestion methods. RESULTS The OT content of the milk samples was similar regardless of OT injections used. Further, OT was found to be stable to heat treatment and gastric pepsin digestion while it was rapidly digested during the simulated intestinal digestion. Reduced OT was digested by pepsin, implying that internal disulphide bridge of OT rendered the peptide resistant to peptic digestion. On the other hand, phenylmethylsulphonyl fluoride (PMSF), a serine protease inhibitor, abrogated the pancreatin induced digestion of OT. INTERPRETATION & CONCLUSIONS These findings suggest that exogenous OT injections do not influence its content in milk. Further, OT present in milk is rapidly degraded during intestinal digestion, ruling out its intestinal absorption and associated adverse health consequences, if any.