[Milk ejection induced by PGF2 alpha during the first two months following insemination of cows. Application to...

Milk ejection after intrajugular injection of 256 micrograms of a synthetic PGF2 alpha analogue (Dinolytic, Upjohn) was measured every 2 days until D60 in 7 pregnant cows and until D25 in 5 non pregnant inseminated cows (trial 1). There was a very close correlation (r around + 0.98) between the values of the 3 parameters used to characterize milk ejection, i.e. amplitude of intramammary pressure deflection, surface area under the pressure curve, alveolar milk volume collected by a teat probe. In the two groups of animals, these values behaved similarly until D15 with a sudden increase between D2 and D7. From D15 they decreased abruptly in females where insemination had failed while they still remained at a high level until D25 (then decreasing until D60) in those presumed to be pregnant (fig. 2). These responses were assumed to result from the release of luteal oxytocin and it is suggested that a single injection of 256 micrograms of Dinolytic on D20, together with milk ejection control using a teat probe, would be a rapid, little expensive method for the farmer (without risks of luteolysis) (trial 2 and fig. 3) to distinguish between pregnant and non pregnant cows.