An investigation into the relationship between milk progesterone concentrations in fore-milk and composite milk samples

Abstract

AbstractMilk progesterone concentrations are generally estimated on a composite, “jar”, sample from the bulk milk collecting jar, with concentrations >3 ng/ml considered as indicative of the presence of luteal tissue. However, on a number of dairy farms composite sampling is not possible as they operate a direct pipeline milking system, without milk meters, and the only practical means of obtaining a milk sample is via fore-milk sampling. The objective of this study was to investigate the relationship between progesterone concentrations, as estimated by an ELISA procedure, in fore-milk strippings and composite milk samples. A significant relationship (r2 = 0.83) was obtained between the progesterone concentration in composite milk and fore-milk samples; y = 1.52 - 1.41(0.163)x, where y = log10(composite progesterone) and x = log10(fore-milk progesterone). A milk progesterone concentration of 3 ng/ml in composite milk corresponded to a milk progesterone concentration of 1.47 ng/ml in fore-milk. Using this relationship progesterone profiles may be compared between herds where milk samples have been obtained by either composite milk or fore-milk sampling. In addition, composite milk samples only should be used with qualitative on-farm assays.