Revue Méd. Vét., 2015, 166, 3-4, 90-95 KACAR (C.) AND COLLABORATORS 90 Introduction he Ovsynch protocol developed by Pursley et al. [21] is known as timed artiicial insemination (TAI). his protocol stimulates bovine ovulation by means of the sequential administration of GnRH, followed by PGF 2α seven days later, and lastly, a inal GnRH injection 48 hours ater the PGF 2α injection. In a previous study conducted to determine the optimum insemination time in cows, pregnancy rates were found to be high during the 16 hours post-administration of the inal GnRH dose, while pregnancy rates were observed to have fallen in procedures performed ater 24 hours [23]. In lactating cows, the use of the Ovsynch protocol between days 5 and 12 of the cycle increased pregnancy rates at a higher level, compared to its use at any other time of the cycle [29]. When the Ovsynch protocol is initiated at any time during the cycle, the synchronization rates achieved ater administering a second GnRH dose are reported to vary between 71.4 and 87% [9, 15, 29]. he injection of a single dose of PGF 2α 10 or 12 days prior to the Ovsynch protocol is reported to improve pregnancy rates in cows [5, 19]. he injection of a single dose of PGF 2α 3 days, 10 days, or 12 days prior to timed artiicial insemination has been reported not to produce successful results for pregnancy rates [4, 16, 17]. Cartmill et al. [4] ABSTRACT he objective of this study was to evaluate pregnancy rates to timed artiicial insemination (TAI) following presynchronization with a single dose of PGF 2α ten days before CoSynch-56 protocol in Brown Swiss crossbred cows and heifers. Group I (GI) cows (n=89) and heifers (n=39) received PGF2α ten days prior to Cosynch-56 protocol while Group II (GII) cows (n=82) and heifers (n=38) received CoSynch-56 protocol only. Pregnancy was evaluated using ultrasonography 30-35 days ater TAI. Pregnancy rates did not difer signiicantly between GI and GII (34.4% and 28.3 %, respectively, P>0.05). However, pregnancy rates difered signiicantly (P<0.05) between cows and heifers in GII (34.1% and 15.7%, respectively). Furthermore, pregnancy rates of heifers in GI was signiicantly higher than that of heifer in GII (P<0.01, 41.0% and 15.7%, respectively). Notably, pregnancy was not achieved in GII heifers with plasma P4 values < 1ng/ml. In conclusion, presynchronization with PGF 2α before Cosynch-56 protocol did not enhance pregnancy rates in Brown Swiss cows but did in heifers. Also, high P4 levels may enhance overall pregnancy rates of cows and heifers subjected to the Cosynch-56 protocol. Keywords: cow, heifer, presynch, Cosynch-56, pregnancy rate RÉSUMÉ Les efets du protocole Cosynch-56 sur le taux de gestation de vaches et génisses pré-synchronisées avec une dose unique de PGF2α L’objectif de cette étude était d’évaluer le taux de gestation après insémination artiicielle (TAI) suite à une présynchronisation avec une dose unique de PGF 2α dix jours avant un protocole Cosynch-56 chez des vaches et génisses croisées de race Brown Swiss. Le groupe I (GI) constitué de 89 vaches et de 39 génisses a reçu une injection de PGF 2α dix jours avant le protocole CoSynch-56 tandis que le groupe II (GII) constitué de 82 vaches et de 38 génisses a suivi le protocole Cosynch-56 seul. La gestation a été évaluée en utilisant l’échographie 30-35 jours après TAI. Les taux de gestation ne difèrent pas signiicativement entre GI et GII (34,4% et 28,3%, respectivement). Cependant, le taux de gestation diférait signiicativement (P <0,05) entre les vaches et les génisses en GII (34,1% tt 15,7%, respectivement). En outre, les taux de gestation chez les génisses en GI était signiicativement plus élevée (P <0,01) que celui des génisses en GII (41,0% et 15,7%, respectivement). La gestation n’a pas été observée chez les génisses GII ayant des concentrations plasmatiques en progestérone <1 ng/ ml. En conclusion, la présynchronisation avec PGF 2α avant un protocole Cosynch-56 a pas amélioré le taux de gestation chez les génisses croisées Brown Swiss mais pas chez les vaches. En outre, les niveaux de progestérone élevés améliorent le taux de gestation chez les vaches et génisses soumis au protocole Cosynch-56. Mots-clés: vache, génisse, présynchronisation, Cosynch-56, gestation, progestérone The effects of Cosynch-56 protocol on pregnancy rates of cows and heifers presynchronized with a single dose of PGF 2α C. KACAR 1 , N. C. LEHIMCIOGLU 2 , H. ORAL 1 , S. YILDIZ 2 , S. KAYA 1 *, M. KURU 1 , A. K. ZONTURLU 3 , S. M. PANCARCI 4 , O. GUNGOR 5 , S. ASLAN 6 1 Department of Obstetrics and Gynecology, Faculty of Veterinary Medicine, University of Kakas, 36300, Kars, Turkey 2 Department of Artiicial Insemination and Reproduction, Faculty of Veterinary Medicine, University of Kakas, 36300, Kars, Turkey 3 Department of Obstetrics and Gynecology, Faculty of Veterinary Medicine, University of Harran, 63200, Sanliurfa, Turkey 4 Department of Obstetrics and Gynecology, Faculty of Veterinary Medicine, University of Balikesir, 10145, Balikesir, Turkey 5 Department of Obstetrics and Gynecology, Faculty of Veterinary Medicine, University of Mehmet Akif Ersoy, 15030, Burdur, Turkey 6 Department of Obstetrics and Gynecology, Faculty of Veterinary Medicine, Universty of Ankara, 06110, Ankara, Turkey *Corresponding author: semra-kakas@hotmail.com 1 his study has been presented as oral communication in the “4th Congress of Veterinary Gynecology” Antalya, Turkey, 4-7 November 2010