LUTEAL FUNCTION IN THE MERINO EWE AND THE EFFECT OF EXOGENOUS PROGESTAGEN

Abstract

SUMMARY Progesterone levels were determined in the ovarian and jugular vein plasma and the corpus luteum of 68 cyclic Merino ewes (controls) and of 32 ewes which had been treated with intravaginal sponges containing a synthetic progestagen (Cronolone, Searle). The weight and diameter of the corpus luteum and the rate of flow of the ovarian vein blood were also recorded. No corrections for procedural losses were made. The control ewes showed highly significant (P < 0·001) cyclic changes in the progesterone contents of the ovarian vein plasma and the corpus luteum, and in the mass of the corpus luteum. There were positive correlations (P < 0·001) between ovarian vein plasma progesterone concentration and the weight (r = 0·651), diameter (r = 0·692), total progesterone content (r = 0·775) and progesterone concentration (r = 0·574) of the corpus luteum. Cyclic changes in the progesterone content of the jugular vein failed to attain significance (0·1 < P < 0·2) but the levels were positively correlated with those in the ovarian vein (r = 0·465, P < 0·001) and with weight (r = 0·432, P < 0·001) and diameter (r = 0·303, P < 0·05) of the corpus luteum. The Cronolone-treated ewes showed cyclic changes in luteal function similar to those in controls, with the exception of animals treated on the day of oestrus. In ewes in which ovulation was not suppressed, the duration of activity of the corpus luteum, as measured by progesterone concentration in ovarian vein plasma, and concentration and content in the corpus luteum was significantly reduced. By the 12th day of the cycle the corpus luteum had almost completely regressed both morphologically and functionally.