Pakistan Journal of Biological Sciences1028-88801812-5735Asian Network for Scientific Information10.3923/pjbs.2007.3620.3625KarimiA. ShabankarehH. KaramiMoeiniM. M.1220071020This study was carried out to evaluate the effects of different levels of GnRH in different days of reproductive cycle on progesterone concentration in dairy heifers. Two hundred heifers were divided into ten experimental treatment: control group with no injection 1) administration of 2.5 mL Gonadorelin (a GnRH analogue) in day of insemination 2) administration of 5 mL GnRH in day of insemination 3) administration of 10 mL GnRH in day of AI insemination 4) administration of 2.5 mL GnRH in day 5 post-insemination 5) administration of 5 mL GnRH in day5 post-insemination 6) administration of 10 mL GnRH in day5 post-insemination 7) administration of 2.5 mL GnRH in day 12 post-insemination 8) administration of 5 mL GnRH in day 12 post-insemination 9) administration of 10 mL GnRH in day 12 post-insemination. Blood samples were collected in days 0, 5, 12 and 19 post insemination (AI = Day 0) for analysis of serum P4 concentration. There was no significant difference among experimental groups on day of insemination. Evaluation of P4 concentration on day 19 illustrated differences in progesterone concentration between groups on day 19 post-insemination. P4 concentration of serum in the day 19 post-insemination significantly increased in groups either by 5 or 10 mL injection of GnRH whether in day 5 or 12 post-insemination versus control group (9.24±2.2, 8.6±1.96, 9.43±2.15 and 9.42±2.14 versus 5.5±0.8, respectively; p<0.05). GnRH administration in the day 5 and 12 post-AI significantly increased progesterone concentration that may decline early embryonic death and improve pregnancy rate.]]>Ambrose, J.D., M.F.A. Pires, F. Moreira, T. Diaz, M. Binelli and WW. Thatcher,19985011571170Beck, N.F.G., A.R. Peters and S.P. Williams,199458243247Binelli, M., W.W. Thatcher, R. Mattos and P.S. Baruselli,20015614511463Butler, W.R., J.J. Calaman and S.W. Beam,199674858865Cam, F., D. Vigo, M. Battochio, M. Faustini, M.C. Veronesi and G. Maffeo,200237294298Cartmill, J.A., S.Z. El-Zarkouny, B.A. Hensley, G.C. Lamb and J.S. Stevenson,20018410511059Chenault, J.R., D.D. Kratzer, R.A. Rzepkowski and M.C. Goodwin,1990348198Coulson, A., D.E. Noakes, J. Hamer and T. Cockrill,1980107108109Drew, S.B. and A.R. Peters,1994134267269Duncan, D.B.,195511142Farin, M.D., G.E. Lamming, W. Haresign,19884310191030Graham, J.D. and C.L. Clarke,199718502519Grohn, Y.T. and P.J. Rajala-Schultz,200060-61605614Hansen, P.J. and C.F. Arechiga,1999773650Jubb, T.F., D. Abhayaratne, J. Malmo and G.A. Anderson,199067359361Kaim, M., A. Bloch, D. Wolfenson, R. Braw-Tal, M. Rosenberg, H. Voet and Y. Folman,20038620122021Lamming, D.,1989202739745Larson, J. and J. Sirois,19975815271532Less, M.C., J.D. Savio, L. Badinga, R.L. de La Sota and W.W. Thatcher,19927036153626Lopez-Gatius, F., P. Santolaria, A. Martino, F. Deletang and F. de Rensis,200665820830Lucy, M.C.,20018412771293MacMillan, K.L., V.K. Taufa and A.M. Day,198611110Mann, G.E., G.E. Lamming and M.D. Fray,199537121131Mann, G.E. and G.E. Lamming,2001121175180McEvoy, T.G., J.J. Robinson and I.S. Robertson,1984in vitro development of ova collected from superovulated ewes.]]>43276276Mee, M.O., J.S. Stevenson, R.K. Scoby and Y. Folman,19907315001507Moreira, F., C. Orlandi, C.A. Risco, R. Mattos, F. Lopes and W.W. Thatcher,20018416461659Nanda, A.S., W.R. Ward, P.C. Williams and H. Dobson,1988122155158NRC,20017th Edn.,Pages: 405Pages: 405Peters, A.R., L. Dwyer, P.A. Canham and J.D. Mackinnon,2000147649652Peters, A.R.,200588155167Rajarnahendran, R., J.D. Ambrose, E.J.P. Schmitt, M.J. Thatcher and W.W. Thatcher,19985011411155Ryan, D.P., S. Snijders, T. Condon, M. Grealy, J. Sreenan and K.J.O. Farrell,199434179191Santos, J.E.P., W.W. Thatcher, L. Pool, M.W. Overton and J.P. Reynolds,20002000pp: 144Santos, J.E.P, S.O. Juchem, R.L.A. Cerri, K.N. Galvao and R.C. Chebel et al.,200487868881Schmitt, E.J., T. Diaz, C.M. Barros, R.L. De la Sota and M. Drost et al.,19967410741083Sheldon, I.M. and H. Dobson,1993133160163Starbuck, G.R., A.O. Darwash, G.E. Mann and G.E. Lamming,20012001pp: 447-450pp: 447-450Starbuck, M.J., R.A. Dailey and E.K. Inskeep,2004842739Stevenson, J.S., E.P. Call, R.K. Scoby and A.P. Phatak,19907317661772Stevenson, J.S., A.P. Phatak, I. Rettmer and R.E. Stewart,19937625362547Thatcher, W.W., K.L. MacMillan, P.J. Hansen and M. Drost,198931149164Thatcher, W.W., C.R. Staples, G. Danet-Desnoyers, B. Oldick and E.P. Schmitt,1994721630Thatcher, W.W., F. Moreira, J.E.P. Santos, R.C. Mattos, F.L. Lopes, S.M. Pancarci and C.A. Risco,2001557589Thatcher, W.W., T.R. Bilby, J.A. Bartolome, F. Silvestre, C.R. Staples and J.E.P. Santos,2006653044Ullah, G., J.W. Fuquay, T. Keawkhong, B.L. Clark, D.E. Pogue and E.J. Murphey,19967919501953Wielbold, J.L.,198884393399Willard, S., S. Gandy, S. Bowers, K. Graves and A. Elias et al.,20035917991810