Pakistan Journal of Biological Sciences1028-88801812-5735Asian Network for Scientific Information10.3923/pjbs.2006.1552.1555ShahnehAhmad ZareTajangookehHamid DeldarPanahHasan SadeghiSakiAli Asghar8200698The objectives of this study were to determine the effects of Controlled Internal Drug Release (CIDR) device treatment duration and equine chorionic gonadotropin (eCG) dose on induction of synchronized fertile estrus and pregnancy, lambing and twinning rates and lamb crop in seasonally anestrous fat-tailed ewes. A total of 73 nonlactating fat-tailed Mehraban ewes (2-5 year old) were assigned to 5 randomized treatments including: 1) 7 days CIDR plus 400 IU eCG (n = 10); 2) 7 days CIDR plus 600 IU eCG (n = 10), 3) 12 days CIDR plus 400 IU eCG (n = 10); 4) 12 days CIDR plus 600 IU eCG (n = 10); 5) nor CIDR and neither eCG (control group, n =33). Overall pregnancy rates in hormone-treated groups (1-4) were higher than in control ewes (p<0.05). Pregnancy rates from first service period in ewes treated for 7 days were higher than in ewes treated for 12 days (p<0.05). The number of estrus to conception and interval from ram introduction to lambing in hormone treated were lower than in control ewes (p<0.05), but did not differ among hormone-treated groups (p<0.05). The highest lambing rates were observed in ewes treated with 600 IU eCG (groups 2 and 4) (p<0.05) compared to the control and other treatment groups. A non-significant increase of twinning rate was observed in groups treated with 600 IU eCG in comparison to other groups. The highest lamb crops were observed in ewes treated with CIDR for 7 days and 600 IU eCG (p<0.05).]]>Ainsworth, L. and J.N.B. Shrestha,198524479487Allison, A.J. and T.J. Robinson,197022515531Burke, V. and D.H. Keisler,198866435435Caraty, A. and D.C. Skinner,1999140165170Fabre-Nys, C. and G.B. Martin,1991130367379Fitzgerald, J.A. and J.N. Stellflug,199169264275Johnson, S.K., R.A. Dailey, E.K. Inskeep and P.E. Lewis,1996136979Knights, M., T. Hoehn, P.E. Lewise and E.K. Inskeep,20017911201131Leyva, V., B.C. Buckrell and J.S. Walton,199850377393O`Mary, C.C., A.L. Pope and L.E. Casida,19509499503Powell, M.R., M. Kaps, W.R. Lamberson and D.H. Keisler,19967422922302Quinlivan, T.D. and T.J. Robinson,19671967pp: 177-194pp: 177-194Safranski, T.J., W.R. Lamberson and D.H. Keisler,19927029352941Signoret, J.P.,19901990pp: 59-70pp: 59-70Van Cleeff, J. and F.J. Karsch and V. Padmanabhan,1998152334Wheaton, J.E., H.F. Windels and L.J. Johnston,19927026282635Wheaton, J.E., K.M. Carlson, H.F. Windels and L.J. Johnston,199333127141Wildeus, S.,200077114