The overall objectives of this thesis were 1) to compare the effect of an additional prostaglandin F2α (PGF2α) treatment and an increased dosage of PGF2α on d 7 during an Ovsynch protocol with an untreated control group, regarding luteolysis and reproductive performance; 2) to determine the effect of progesterone (P4) supplementation by means of a P4 releasing intravaginal device (PRID) insert for 8 days during an Ovsynch protocol on pregnancy per artificial insemination (P/AI) and pregnancy loss; 3) to evaluate vaginal discharge at device removal on fertility, and 4) to evaluate the diagnostic performance of transrectal ultrasound to detect a functional corpus luteum (CL) based on circulating P4 levels. In the first study, the aim was to compare the effect of two PGF2α treatments 24 h apart (25 mg of dinoprost at d 7 and 8) and the treatment of a double PGF2α dose (50 mg of dinoprost at d 7) with a control group (25 mg of dinoprost at d 7) during a 7-d Ovsynch protocol with inclusion of a PRID device for 8 days on luteal regression and P/AI in lactating Holstein cows. Furthermore, we wanted to evaluate the potential impact of vaginal discharge caused be the P4 insert on fertility and whether serum P4 levels correspond with ultrasound CL diagnostic. The experiment was conducted on a single commercial farm in Northeast Germany. A total of 1,056 cows were randomly assigned within parity to receive 1 of 3 Ovsynch protocols on a weekly basis: 1) a control group in which cows received an Ovsynch protocol with a single PGF2α treatment (control: d 0, 100 μg of GnRH + PRID; d 7, 25 mg of dinoprost; d 8, PRID removal; d 9, 100 μg of GnRH), 2) an Ovsynch protocol with a double dose of PGF2α (DoubleDose: d 0, 100 μg of GnRH + PRID; d 7, 50 mg of dinoprost; d 8, PRID removal; d 9, 100 μg of GnRH) and 3) an Ovsynch protocol with an additional PGF2α treatment 24 h after the first one (2PGF: d 0, 100 μg of GnRH + PRID; d 7, 25 mg of dinoprost; d 8, 25 mg of dinoprost and PRID removal; d 9, 100 μg of GnRH). All cows received a PRID from d 0 until removal on d 8, on which vaginal discharge was evaluated and scored [vaginal score (VS) 0 = no debris, VS 1 = small flecks of purulent debris, VS 2 = abundant amount of purulent debris]. To facilitate first post partum timed AI (TAI), the farm used a Presynch-Ovsynch protocol (PGF2α, 14 d later PGF2α, 12 d later start of an Ovsynch protocol). All cows were inseminated approximately 16 h after the second GnRH treatment (G2) of the Ovsynch protocol. Ovarian ultrasonography was performed on d 0 (G1) to determine abence or presence of a CL and its size. Blood samples were collected on d 0, 7 and 9 in order to asses P4 concentrations. Pregnancy diagnosis was performed using transrectal ultrasound d 38 ± 3 after AI and reconfirmed d 80 ± 7. Treatment affected P4 concentration at G2. Mean P4 concentrations at G2 differed (P = 0.037) among treatments (control 0.35 ± 0.02 ng/mL; DoubleDose 0.29 ± 0.02 ng/mL; 2PGF 0.30 ± 0.02 ng/mL) and were lower for 2PGF cows (P = 0.043) and DoubleDose cows (P = 0.023) compared with cows in the control group. There was an interaction between treatment and CL at G1 (P = 0.087). Cows without a CL at initiation of the protocol had decreased (P = 0.014) P4 concentrations when treated with a double dose of PGF2α and tended (P = 0.062) to have a decreased P4 concentration at G2 when receiving 2 consecutive treatments 24 h apart. Proportion of cows with luteolysis differed among treatments (P = 0.025; control 84.8%; DoubleDose 91%; 2PGF 92.6%) considering only cows with P4 concentrations above 1.0 ng/mL (indicative of presence of a CL) at first PGF2α (863/1011) and 0.5 ng/mL at G2 (indicative of complete luteolysis). Cows that received an additional treatment 24 h apart had greater P/AI (46.5%) compared with DoubleDose cows (37.7%; P = 0.045), but did not differ compared with cows in the control group (40.3%; P = 0.144). Considering luteal status at G1, cows within the 2PGF group had greater (47.9%; P = 0.043) P/AI when compared with DoubleDose cows (32.7%), but did not differ compared with control cows (36.1%; P = 0.109) when no CL was present at protocol initiation. The overall accuracy was 87.2% to identify a functional CL using transrectal ultrasound at the beginning of the protocol. The area under the curve (AUC) was 0.901 and can be considered highly accurate. The optimum cutoff was a 20-mm diameter of the CL. Vaginal discharge score had a significant association (P = 0.001) with P4 concentrations at the first PGF2α treatment. Cows assigned to a VS of 2 had greater (4.3 ± 0.2 ng/mL) serum P4 levels than cows assigned to score 0 (3.0 ± 0.3 ng/mL; P = 0.001) and 1 (3.7 ± 0.1 ng/mL; P = 0.002). Progesterone concentration at d 7 was greater (P = 0.027) for cows assigned to VS 1 compared with cows assigned to VS 0. Vaginal discharge score at PRID removal tended to have an association with P/AI at d 38 after AI (P = 0.072). Pregnancy per AI did not differ (P = 0.459) among cows scored with a VS of 0 and 1 [36.5% (25/69); 41.3% (320/780)], but was significantly greater [49.7% (102/207)] for cows having a VS of 2 compared with VS 1 (P = 0.039), and tended to be greater compared with VS 0 (P = 0.066). Outcomes from this study demonstrate that both PGF2α modifications can increase luteolysis in P4 supplemented Ovsynch protocols compared with a standard PGF2α treatment on d 7 of the protocol. Interestingly, only cows receiving an additional PGF2α treatment had a numerical increase in P/AI (6.2 %), especially in cows without a CL at G1 (11.8 %), whereas an increased dose of PGF2α did not lead to any improvement in reproductive performance. Vaginal discharge at d 8 of the protocol, after PRID removal, was associated with higher P4 concentrations at d 7 and greater P/AI. Ultrasound can be deemed as a valuable tool for CL detection. The second study aimed to elucidate the effect of P4 supplemention for 8 days, by means of a PRID insert, during an Ovsynch protocol on P/AI and pregnancy loss compared with a standard 7-d Ovsynch protocol. A total of 716 lactating Holstein cows from one commercial dairy farm in Northeast Germany were enrolled in this study. The treatment group was part of the aforementioned study and received an 8-d P4-based Ovsynch protocol (PRIDsynch: d 0, 100 μg of GnRH + PRID; d 7, 25 mg of dinoprost; d 8, PRID removal; d 9, 100 μg of GnRH), whereas the control group received a standard 7-d Ovsynch protocol as part of the farms reproductive schedule (control: d 0, 100 μg of GnRH; d 7, 500 μg of cloprostenol; d 9, 100 μg of GnRH). All cows were inseminated approximately 16 h after G2. Pregnancy diagnosis was performed by transrectal ultrasound examination d 38 ± 3 after AI and reconfirmed d 80 ± 7. Pregnancy loss included cows that experienced pregnancy loss from d 38 to 80. Results from this study demonstrate the overall beneficial effect of an elongated P4, 8 d supplementation with a PRID insert in an Ovsynch protocol on reproductive performance. Pregnancy per AI was significantly increased in PRIDsynch cows [P = 0.014; 38.9 % (115/360)] compared with untreated control cows [31.7 % (115/360)] on d 38 ± 3 after AI. However, pregnancy loss was not affected by treatment [P = 0.279; control: 8.8 (10/113) vs. PRIDsynch: 6.2 (9/146)]. Overall, this thesis shows that 1) the proportion of cows with complete luteal regression near TAI was increased by both PGF2α modifications, but only the second treatment 24 h apart resulted in greater P/AI compared with the increased PGF2α dose and a numerical increase in P/AI compared with control cows, especially in cows lacking a CL at protocol initiation, 2) the addition of a PRID from d 0 until removal on d 8 of the TAI protocol increased reproductive performance but did not influence pregnancy loss, 3) vaginal discharge caused by P4 inserts has no negative impact on fertility and 4) ovarian ultrasound examinations are suitable for detection of a functional CL. Taken together, these results have a potential to improve reproductive performance on dairy farms using TAI protocols.weiterlesen