Numbers of steroidogenic luteal cells in Booroola Merino ewes

Summary. In Exp. 1 ovulation rates, plasma concentrations of progesterone, mean individual and total CL weights were determined on Days 4, 10 and 12 after oestrus of Booroola Merino ++ ewes and FF ewes. Mean ovulation rates ranged from 1·5 to 1·8 in ++ ewes and from 5·3 to 6·2 in FF ewes (P < 0·01). There were no differences in plasma concentrations of progesterone or total luteal weight between the two groups on any of the days studied. Individual CL were smaller (P < 0·01) in FF ewes than in ++ ewes. In Exp. 2 the numbers of luteal cells in CL collected from 5 ++ and 5 FF ewes on Day 10 of the oestrous cycle were morphometrically determined. The CL from FF ewes were smaller (P < 0·01) and had fewer total steroidogenic cells (P < 0·01), fibroblasts (P < 0·01), and capillary endothelial cells and pericytes (P < 0·05). However, the luteal cell volume density, number of cells/g tissue, average cell diameter or average cell volume was not different between the two groups of ewes for any cell type studied. It is concluded that the 5–6 CL in FF ewes function in an identical fashion to the 1–2 CL in ++ ewes. Keywords: Booroola ewes; luteal cells; steroidogenesis