Abstract
The aim of the current study was conducted to improve the first insemination conception rate in Holstein dairy cows by the use of estradiol benzoate and antioxidants in conjunction with ovsynch program. A total number of 160 cyclic dairy cows 55-67 day in milk, 4-10 years old, 2nd to 5th lactations were divided into 4 groups: G1 (n=40) treated with ovsynch program (control group). G2 (n=40) injected with 1mg estradiol benzoate i.m at the time of estrumate injection in ovsynch protocol, G3 (n=40) injected with 15ml of vitesel i.m at the time of estrumate injection in ovsynch protocol, G4 (n=40) injected with 1mg of estradiol benzoate plus 15ml vitesel i.m at the time of estrumate injection in ovsynch protocol. The expression ad intensity of estrus signs were studied using behavioral and physiological changes. The conception rate after first insemination examined using transrectal ultrasonography on the 30th day from insemination and pregnancy rate was confirmed rectally after 60 days from insemination. The obtained results showed that total cows expressed estrus in G2 (ovsynch plus estradiol benzoate) and G4 (ovsynch plus estradiol benzoate and E-selenium) had highly significantly incidence (87.5% and 95.0%) compared with the cows of G1 (ovsynch group) and G3 (ovsynch plus E-selenium) 52.5% and 60%) P < 0.0001.
The G2 and G4 had significant incidence of intense estrus signs (82.9% and 84.2%) compared with cows of G1 and G3 (57.1% and 62.5%) p = 0.040. also, it was noted that the G2 and G4 had highly significant incidence of first insemination conception (75.5% and 80%) versus (32.5% and 40%) in cows of G1 and G3 P < 0.0001. the pregnancy rate in G2 and G4 had highly significant incidence (67.5% and 80%) versus (30% and 40%) in cows of G1 and G3 P < 0.0001 as shown in table 2. Moreover, all cows showed intense estrus signs had 100% first insemination conception rate compared with 6.7% in weak estrus signs as in (table 3 and figure 1). It can be concluded that the beneficial effects of injection of estradiol benzoate and antioxidant with ovsynch program improve the reproductive efficiency through intensified signs of estrus and increase secretary activity of the tubular tract. These drugs improve the first insemination conception, pregnancy rates and enhances fertility in postpartum Holstein dairy cows.

Key words: ovsynch – Estradiol benzoate – antioxidants – estrus intensity – conception rate – dairy cows