Comparative Studies of Ovarian Steroids in Blood, and Specific Proteolytic Enzymes in the Cervical Mucus, in Four Sheep Breeds after Oestrus Synchronization (Progesterone and PMSG). 1. Breed Variation of Oestradiol‐17ß and Progesterone in Blood during Nat

Contents The concentrations of oestradiol‐17β and progesterone in the blood were studied during natural oestrus, synchronized oestrus, and the first oestrus after synchronized oestrus in four sheep breeds (Friesland, Chios, Serres and Karagouniki). During natural oestrus, significant variations of oestradiol‐17β concentration were only seen in Karagouniki ewes; during synchronized oestrus, oestradiol‐17β concentration in the blood showed a gradual decrease in all breeds. However, during the first oestrus after synchronized oestrus, the concentration of oestradiol‐17β in the blood returned to normal in all but the Serres breed.The concentration of progesterone in the blood showed no variation during natural oestrus, but, during synchronized oestrus, significant variations of progesterone in the blood were seen in all but the Serres breed. During the first oestrus after the synchronized oestrus, the progesterone in the blood returned to the natural‐oestrus levels with, however, some differences among the breeds.Oestrous synchronization therefore disturbed the con‐centration of oestradiol‐17P and progesterone in the blood of the ewe in a varying way, depending on the breed.