الفهرس 
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Abstract
Two hundred cows were used for double Ovsynch program. As shown in Table 1, the number of cows which did not exhibit estrus signs after the first injection of GnRH (day 0 of the program) was 178 (89.00%). After PG F2α injection on day 7, the number of cows which did not exhibit heat was further decreased from 178 to 130 (65.00 %). The second dose of GnRH on day 10 could decrease the number of anestrum cows to 88 (44.00%). This number was decreased after injection of GnRH on day 17 from 88 to 70 (35.00%). Injection of PGF2α on day 24 further decreased the number of anestrum cows to 46 (23.00%). After the final injection of GnRH on day 26, the remaining number of cows for fixed time insemination was 44 (22.00%). In conclusion, double- Ovsynch protocol can be used as an efficient tool for improving the fertility in postpartum animals especially in first lactation cows and during summer season (heat stress) and its beneficial role is probably attributed to its hormonal effect.