Insemination Behaviour Ovary in Pre-oestrus: The yellow body (corpus luteum) has shrunk enormously under the influence of the prostaglandin F2 alpha. A dominant Graafian follicle starts to grow. It is smooth and rounded ("like a watch glass") with a diameter of over 1 cm. Ovary Uterus and vagina Hormones Instruction manual Pre-oestrus Oestrus Post-oestrus Inter-oestrus/Dioestrus