Progesterone concentration as an indicator of ovarian response to superovulation in Chios ewes G.S. Amiridis a,* , C.A. Rekkas b , G.C. Fthenakis a , E. Vainas b , A. Lymberopoulos b , V. Christodoulou c , S. Belibasaki b a Faculty of Veterinary Medicine, Department of Reproduction and Obstetrics, University of Thessaly, P.O. 199, 43100 Karditsa, Greece b Veterinary Research Institute, N.AG.RE.F., Ionia, Greece c Instituteof Animal Husbandry, N.AG.RE.F., Paralimni, Greece Received 24 April 2001; accepted 18 July 2001 Abstract We investigated the prediction of the ovarian response to superovulation using progesterone P 4 ) determination in Chios ewes. During the estrus period, estrus synchronization and multiple ovula- tions were induced in 100 non-pregnant, non-lactating Chios ewes by a combination of FGA- impregnated intravaginal sponges and 8.8 mg of ovine FSH. Laparoscopic insemination was conducted 24±28 h after the onset of estrus. A concentration of P 4 was determined on Day 5 of theestrouscycleandonDay6theovarianresponsewasevaluatedbycountingthecorpusluteaCL); subsequently, embryo collection was performed. According to the response of their ovaries, ewes wereallocatedintofourgroups:An 30);Bn 37);Cn 22);Dn 11),withminimal0±3 CL), moderate 4±8 CL), good 9±13 CL) or extreme >13 CL) ovarian response, respectively. In groups C and D, the mean blood serum P 4 concentration 23.2 and 27.3 ng/ml, respectively) was higherP < 0:001)thanthatingroupsAandB4.6and13.1ng/ml,respectively);nodifferencewas detected in blood P 4 concentration between groups C and D. A strong linear relation F < 0:00005) wasfoundbetweenbloodP 4 concentrationandthenumberofCL,aswellasbetweenbloodP 4 anda dummyvariablecorrespondingtopoor<4CL)ormoderate/good/extremeovarianresponse>3CL). Our results indicate that based on blood P 4 measurement, it is feasible to identify ewes that should show the highest embryo recovery, while it is impossible to predict the exact number of CL formed. # 2002 Elsevier Science Inc. All rights reserved. Keywords: Sheep reproduction; Superovulation; Progesterone; oFSH Theriogenology 57 2002) 1143±1150 * Corresponding author. Tel.: 30-441-660-73; fax: 30-441-660-77. E-mail address: gsamir@vet.uth.gr G.S. Amiridis). 0093-691X/02/$ ± see front matter # 2002 Elsevier Science Inc. All rights reserved. PII:S0093-691X01)00706-3