The aims of this study were to determine the relationship between the ultrasonographic determination of corpora lutea and the plasma progesterone profile of cyclic cows during an oestrous cycle, and to compare the accuracy of detection of normal and abnormal ovarian structures by ultrasonography and palpation per rectum, based on the plasma progesterone profile. The ovaries of six lactating cyclic dairy cows were scanned and blood samples were obtained three times a week for one month. There was a high correlation (r = 0.85) between the diameter of the corpus luteum and the plasma progesterone concentration, but on days -3 and -2 (oestrus = day 0) the diameter was the same as mid-luteal values but it was functionally inactive (plasma progesterone < 0.5 ng/ml). The accuracy of palpation per rectum and ultrasonography for determining the presence and age of the corpora lutea was investigated in 34 cows by using the plasma progesterone concentration and the dissection of ovaries post mortem as standards. The sensitivity, specificity and positive predictive value of palpation for identifying mid-cyclic corpora lutea were 85 per cent, 95.7 per cent and 89.5 per cent, respectively. Ultrasonography had a sensitivity of 95 per cent, a specificity of 100 per cent and a positive predictive value of 100 per cent. Twenty-nine cows were diagnosed by palpation per rectum as having either follicular or luteal cysts. During ultrasonography, an ovarian cyst was defined as a non-echogenic structure at least 5 mm in diameter.(ABSTRACT TRUNCATED AT 250 WORDS)
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