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Abstract: To give a standard in the Iranian Chall ewes, 24 of them weresynchronized by two injections of PGF2a (12.5 mg/ewe Lutalize, Upjohn) 8 dayapart. Forty-eight h after the 2nd injection, 16 ewes showed signs ofestrous and were randomly divided into 2 groups and each was introduced afertile ram for 24 h (ram introducing day was counted as day 0). Embryonic
vesicle (E.V.), biparietal diameter (B.P.D.) and crown ramp length (C.R.L.)were measured. Early pregnancy diagnosis was performed by transrectal (withor without abdominal pressure) ultrasonography in standing position.Ultrasonography was performed until day 144. Embryonic vesicle was 0.55 cmin diameter on the day 18. It was 0.79, 0.95, 1.41, 1.91, 2.42, 2.98 and3.42 cm in days 20, 21, 24, 25, 30, 33 and 37 of pregnancy, respectively.
The first assessment of BPD was in day 37, which was 1.04 cm. It was 1.19,1.87, 4.12 and 6.27 for days 40, 61, 98 and 144 of pregnancy, respectively.CRL was 2.25, 2.78, 3.19, 4.33, 5.39, 6.94 and 8.03 in days 33, 37, 40, 44,47, 54 and 58 of pregnancy. These data are the first report giving astandard measurement in Chall gestational age assessment. J.Vet.Res.
62,2:1-5,2007.