Oestrus synchronization in high lactating dairy cows

This study was conducted to compare a recent method for oestrussynchronization in lactating dairy cows using PGF2α (P), GnRH (G) andestradiol cypionate (ECP). Four treatments were performed on sixty dairy cows. In treatment 1-PP (twice prostaglandin), cows received two injections of PGF2α on days 0 and 11 (n=14). In treatment 2-PGP (prostaglandingonadotropin- prostaglandin), cows were injected twice with 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 (prostaglandin-gonadotropin-prostaglandin-estradiol-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 (prostaglandin-gonadotropinprostaglandin- estradiol-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. Every cow was blood sampled at selected intervals for progesterone and estradiol assay and inseminated at oestrus. After 1st PGF2α injection, a higher percentage of ovulated cows observed with PGP than PP treated cows (64.3 % vs 50 %; P<0.05). The GnRH-treated cows tended to have a larger mature follicle present at 2nd PGF2α injection (71.4 %) than none treated ones (50 %). 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). Submission rates (number of inseminated/total X 100), differed statistically across treatments, especially those treated with ECP, as well as the conception and pregnancy rates observed were higher with the ECP treated cows than the other treatments. In conclusion, PGP protocol seemed to produce more mature follicles and ovulated cows. The combination of ECP and PGP (PGPE-1) enhanced oestrus and increased ovulation, thus it is potentially a new method to routinely synchronize oestrus and ovulation in dairy cows.