Corpus luteum size and plasma progesterone levels in cattle after cloprostenol-induced luteolysis

Abstract

Heifers (n = 11) and cows (n = 6) which had a well-developed corpus luteum (CL) were injected with cloprostenol, and the ultrasonographic CL size (in mm) and plasma progesterone (P4) concentrations (ng/ml) were studied up to Day 7 of the following cycle. Heifers and cows had a correlation coefficient of 0.49 (P<0.05) and 0.26 (P>0.1), respectively, between CL size and plasma P4 concentrations during luteal regression. During the subsequent luteal development, the correlation was 0.47 (P<0.001) in heifers and 0.41 (P<0.01) in cows. It is concluded that ultrasonographic assessment of the CL size is a reliable method for estimating peripheral plasma P4 levels during cloprostenol-induced CL regression and subsequent development in heifers, while the same estimate can only be made during CL development in cows. © 1993.