Effects Of Estrus Synchronization And Ovsynch-Timed Artificial Insemination On Reproductive Performance In Holstein Cows And Heifers

The estrus synchronization and Ovsynch-timed artificial insemination in dairy cattle could make a large group cattle have their estrus in a shorter time after exogenetic hormones treatment, and reduce the workload of estrus detection, even more than without estrus detection in timed artificial insemination(TAI). Therefore, it is important to study the effects of estrus synchronization and Ovsynch-timed artificial insemination on reproductive efficiency in dairy cattle. In order to provide some useful references for reproductive and administrative technicians in dairy farms, this study was carried out to investigate the application of estrus synchronization and Ovsynch-timed artificial insemination with three exogenetic hormones(PGF2α, Gn RH and P4) in Holstein cows and heifers. The results were as follows:Experiment one: Effects of Estrus Synchronization on Reproductive Performance in Holstein Cows152 Holstein milking cows(healthy, medium somatotype and 50 to 85 d postpartum) were randomly assigned into three groups. The cows in experimental groups were treated by PGF2α or CIDR+PG to induce heat synchronization, and the cows in the control group were checked for spontaneous heat. All cows were artificially inseminated according to the a.m.-p.m. rule(8 to 12 hours after onset of heat). Blood samples were collected from the experimental cows at CIDR insertion, PGF2α injection and artificial insemination(AI). The results showed that the estrus synchronization rate of the experimental groups were very significantly higher than that of the control group(P<0.01), but there was no significant difference in non-return rate and conception rate between the experimental groups and the control group(P>0.05). The estrus synchronization rate of the CIDR+PG treated group(93.5%) was very significantly higher than that of the PG treated group(65.6%)(P<0.01). The 21-day pregnancy rate of the CIDR+PG group(38.7%) was significantly higher than that of the control group(16.7%)(P<0.05). The concentration of P4 in serum at AI of the experimental groups were significantly higher than that of the control group(P<0.05), but there was no significant difference in the concentration of E2 in serum at AI between the experimental groups and the control group(P>0.05). There was no significant difference in abortion rate, calving rate, gender ratio, gestation length, birth weight, uterine recovery at 15 d and 30 d postpartum, days to first breeding and the submission rate at 90 d postpartum between the experimental groups and the control group(P>0.05), but the number of healthy cows in uterine recovery at 45 d postpartum of the PG treated group was significantly lower than that of the control group(P<0.05).Experiment two: Effects of Ovsynch-Timed Artificial Insemination on Reproductive Performance in Holstein Cows286 Holstein milking cows(healthy, medium somatotype and 50 to 85 d postpartum) were randomly assigned into three groups. All cows received Gn RH injection followed 7 d later by PGF2α injection and then received one treatment as the followings: The experimental group one, cows received the second Gn RH injection 48 h after PGF2α treatment and timed AI 16~18 h after the second Gn RH injection(Ovsynch); The experimental group two, cows received the second Gn RH injection 56 h after PGF2α treatment and timed AI 16~18 h after the second Gn RH injection(Ovsynch-56); The experimental group three, cows received the second Gn RH injection 72 h after PGF2α treatment and timed AI at the same time(Cosynch-72). Blood and milk samples were collected from the experimental cows at the first Gn RH injection, PGF2α injection, the second Gn RH injection and AI. The results showed that there was no significant difference in the non-return rate(60.9%, 54.8% and 58.2%), conception rate(35.9%, 33.3% and 35.4%) and 21-day pregnancy rate(33.0%, 31.6% and 31.8%) between the three groups(P>0.05). Compared with the spontaneous heat group in Experiment one, the conception rate of TAI programs was lower but the 21-day pregnancy rate of TAI programs was significantly higher(P<0.05). According to the determination result of P4 and E2 in serum, TAI technology could induce cows estrus and ovulation synchronization successfully, but there were some time points that the concentration of P4 and E2 in milk were significantly higher than that of the spontaneous heat group. There was no significant difference in abortion rate, calving rate, gender ratio, gestation length, birth weight, uterine recovery after calving, days to first breeding and the submission rate at 90 d postpartum between the TAI groups and the spontaneous heat group(P>0.05).Experiment three: Effects of Service Times on Reproductive Performance in Holstein Cows Treated with Ovsynch Program132 Holstein milking cows(healthy, medium somatotype and 50 to 85 d postpartum) were randomly assigned into three groups. All cows received the first Gn RH injection, PGF2α injection 7d later and the second Gn RH injection after 48 h PGF2α treatment then received one of the following TAI programs: The experimental group one, cows received timed AI at 5~6 h and 16~18 h respectively after the second Gn RH injection; The experimental group two, cows received timed AI at 16~18 h and 40~42 h respectively after the second Gn RH injection; The control group, cows received timed AI at 16~18 h after the second Gn RH injection. The results showed that there was no significant difference in the non-return rate and conception rate between the experimental groups and the control group(P>0.05), but the conception rate of the experimental groups(43.2% and 48.6%) reached the level of the spontaneous heat group in Experiment one(40%) while the conception rate of the control group was only 34.2%. According to the monitoring results, the conception rate of cows that were detected in estrus was very significantly higher than that of cows were not detected in estrus(61.7% Vs 26.5%, P<0.01), and the time of estrus were mainly concentrated in the second Gn RH injection.Experiment four: Effects of Ovsynch-Timed Artificial Insemination on Reproductive Performance in Holstein Infertility Cows88 Holstein milking cows(healthy, medium somatotype and difficult to mate) were randomly assigned into three groups, which received Ovsynch, CIDR+Ovsynch or CIDR+PG+Gn RH treatment,respectively. Blood samples were collected from 10 cows in CIDR+Ovsynch and CIDR+PG+Gn RH treatment group at CIDR insertion, CIDR remove, the second Gn RH injection and AI to determine the concentration of P4 and E2 in serum.The results showed that the three TAI programs could induce a certain number of infertility cows pregnancy, and there was no significant difference in the non-return rate between the three groups(P>0.05).The conception rate of the CIDR+Ovsynch group(46.7%) had a tendency to be significantly higher than that of the Ovsynch group(28.6%) and the CIDR+PG+Gn RH group(26.7%), but there also was no significant difference(P=0.08, P=0.06). According to the determination results, the trend of the concentration of P4 in serum of the CIDR+Ovsynch group was similar to that of the CIDR+PG+Gn RH group, but the trend of the concentration of E2 in serum depend on the stage of estrous cycle before the beginning of TAI programs. The concentration of E2 in serum of pregnant cows was very significantly higher than that of non-pregnant cows(P<0.01).Experiment five: Effects of Estrus Synchronization and Ovsynch-Timed Artificial Insemination on Reproductive Performance in Holstein Heifers1046 Holstein heifers(healthy, medium somatotype and more than 14 months) imported from Australia were randomly assigned into control group and experimental group. The heifers in the control group were checked for spontaneous heat, and the heifers in the experimental group were treated by Prostaglandin F2α(PGF2α) to induce heat synchronization or treated by different TAI programs(Ovsynch or Ovsynch+CIDR program).The results showed that there was no significant difference in non-return rate and conception rate between the experimental group and the control group(P>0.05), but the 21-day pregnancy rate of the experimental group was significantly higher than that of the control group(P<0.05). There was no significant difference of the estrus synchronization rate between different PG treatments(PG, PG-7-PG and PG-11-PG)(76.1%,81.7% and 84.6%)(P>0.05). There was no significant difference in non-return rate, conception rate and 21-day pregnancy rate in Ovsynch and Ovsynch+CIDR treatment(P>0.05). The conception rate of heifers were significantly affected by different AI technicians(P<0.05), but there was no effect on the conception rate among the frozen semen from different bulls(P>0.05).