Abstract
To evaluate the progesterone-secreting function of the corpus luteum objectively, ultrasonographic measurements were made of the luteal-tissue area and the central luteal cavity; and progesterone concentration (P4) was determined by means of enzyme immunoassay 8 10 days following estrus. Observation of the corpus luteum in 153/154 cows showed plasma P4 concentration of more than 1ng/ml. These concentrations were lowest when the luteal-tissue area was less than 3cm2 and grew higher as that area increased. The presence and size of a central luteal cavity exerted no influence on either plasma P4 concentration or luteal-tissue area. These results suggest that ultrasonographic measurement of the corpus-luteum area is useful in assessing progesterone-secreting ability.
