Abstract
This study was conducted to through the light on a recent method for estrus synchronization in lactating dairy cows using PGF2α, GnRH and estradiol cypionate (ECP). Four treatments were performed on sixty dairy cows. In treatment 1 (PP), cows received two injections of PGF2α on days 0 and 11 (n=14); while in treatment 2 (PGP), cows were injected twice PGF2α on days 0 and 11 and 100 ug of GnRH on day 3 after the 1st injection (n=14). In treatment 3 (PGPE-0), cows were treated with PGP and 1 mg of ECP at the same time of 2nd PGF2α injection (n=16). In treatment 4 (PGPE-1), cows were treated with PGP and 1 mg of ECP one day after 2nd PGF2α injection (n=16). The cows were examined rectally and ultrasonographically by B-mode Ultrasound System [Pie-Medical Scanner-240] with a 6-8 MHz linear rectal transducer. Every cow was blood sampled at selected intervals for progesterone and estradiol assay and inseminated at estrus. The results showed a higher percentage of GnRH-treated cows (PGP) ovulated after 1st PGF2α injection than the non treated (PP) cows (64.3% vs 50%; P<0.05). The GnRH-treated cows tended to have a larger mature follicle present at 2nd PGF2α injection. Subsequently, the percentage of cows that ovulated after 2nd PGF2α injection was 71.4% vs 50% for GnRH-treated cows than none treated ones, respectively. Two days after 2nd PGF2α injection, cows treated with PGP had a higher peak preovulatory concentrations of estradiol compared to PP treated cows (3.2±0.48 vs 2.6±0.45 pg/ml). Additionally, cows treated with ECP (PGPE-0 and PGPE-1) had a higher peak preovulatory concentrations of estradiol (6.3±0.43 and 6.99±0.63 pg/ml; P<0.01); and a higher percentage ovulation (75.0% and 87.5%) than the other treated groups (PP or PGP). Thus, a higher percentage of ECP (especially PGPE-1 group) treated cows were observed in standing estrus and ovulated after 2nd PGF2α injection than the other treated groups. Submission rates (number of inseminated/totalX100), differed statistically across treatments, especially those treated with ECP, as well as; the conception and pregnancy rates were observed higher with the ECP treated cows than the other treatments. In conclusion, PGP protocol increased the number of cows that ovulated after 1st PGF2α injection and produced more mature follicles at the time of 2nd PGF2α injection. The combination of ECP and PGP (PGPE-1) enhanced the expression of estrus and increased ovulation percentage, thus it is potentially a new method to routinely synchronize estrus and ovulation in dairy cows.
Published Version
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