Serum progesterone (P4) concentration was measured using 2 methods, and ovaries were examined by ultrasonography (US) to determine the presence of a corpus luteum (CL) in 101 lactating dairy cows. The concordance correlation coefficient between the 2 methods (Ovucheck and Immulite P4 assays) was high (ρc = 0.94); agreement between the assays on presence of a CL based on P4 > 1 ng/mL was excellent (Kappa = 0.88) and of each assay with US was good (Kappa = 0.63 for each).
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