Comparison of two estrous synchronization protocols on reproductive performance of dairy cows

الملخص EN

Lactating dairy cows (n = 53) were used to evaluate the effect of two estrous synchronization protocols starting between d 10-12 of the estrous cycle on reproductive performance.

Cows in the Ovsynch (Control) treatment n = 24) received an i.

m.

injection of 10μg Gonadotropin Releasing Hormone (GnRH) agonist (Buserelin, Receptal®), followed 7 d later by an i.

m.

injection of 25 mg Prostaglandin F2α (PGF2α) and 48 h later by a second i.

m.

injection of 10μg GnRH.

The protocol was concluded with the timed artificial insemination (TAI) 16-20 h after the second GnRH.

Cows in the Short-ES estrous Synchronization treatment (Short-ES ; n = 29) received an i.

m.

injection of 25 mg PGF2α and an i.

m.

injection of 1 mg estradiol benzoate (EB) dissolved in oil and 10μg GnRH 48 and 60 h after PGF2α, respectively.

These cows were inseminated artificially at detected estrus.

Blood samples were collected from all cows at days 0 (day of AI), 7, 14, 21, 22, and 23 after AI to determine P4 concentrations.

Pregnancy rates from first AI were based on plasma P4 concentrations on d 22 ± 1 post AI, and confirmed by rectal palpation between days 45 and 50 post AI.

Results showed that more (P < 0.01) cows in the Short-ES group (86.2 %) exhibited estrus than in the Ovsynch group (41.7 %).

Pregnancy rates to first AI were greater (P < 0.05) in the Short-ES group (37.4 %) than in the Ovsynch (12.5 %) group.

In contrast, pregnancy losses were lower (P < 0.05) in the Short-ES group (38.9 %) than in the Ovsynch (76.9 %) group.

Pregnancy rates to second, third, and overall pregnancy rates were similar between both groups and between primiparous and multiparous cows.

Days open for pregnant cows tended to be higher (P < 0.09) in the Ovsynch group than in the Short-ES group.

Plasma P4 concentrations were similar between pregnant and nonpregnant cows on days 0 and 7 after AI, however, were greater (P < 0.01) for pregnant than nonpregnant cows on days 14, 21, 22, and 23 after AI.

Results indicate that Short-ES protocol improves reproductive performance by increasing the number of cows exhibiting estrus and pregnancy rates to first AI compared with Ovsynch protocol.