Effect of progesterone supplementation using 2 different intravaginal devices during a 7 day Ovsynch protocol in lactating dairy cows.

The objective of this study was to evaluate the effect of progesterone supplementation using 2 different commercially available intravaginal progesterone (P4) devices during a 7 d Ovsynch protocol on pregnancy per/artificial insemination (P/AI) in lactating dairy cows. We hypothesized that cows receiving an intravaginal device with 1.55 g of P4 have increased P/AI compared with untreated controls or cows supplemented with 1.0 g of P4 and that there is an association between vaginal discharge score (VDS) after removal of intravaginal device and vaginal pH. A total of 731 lactating dairy cows, including 1,064 inseminations were randomly assigned to a modified Ovsynch protocol. Cows in the control group (n = 353) received no P4 supplementation during Ovsynch protocol (control: d 0 GnRH; d 7 PGF; d 8 PGF; d 9 GnRH). Cows in the bovine intravaginal device (DIB) group (n = 354) received an intravaginal P4 releasing device with 1.0 g P4 from d 0 until d 8 during the Ovsynch protocol as described, and cows in progesterone releasing intravaginal device (PRID) group (n = 357) were supplemented with a device containing 1.55 g P4. On d 0, transrectal ultrasound assessment of the ovaries was performed to determine the presence and size of a corpus luteum (CL). On d 8, after removal of the devices, VDS was evaluated and pH value from vaginal discharge was measured. All cows received timed AI ∼16 h after the second GnRH treatment. Pregnancy diagnosis was performed using transrectal ultrasound at d 38 ± 3 after AI and reconfirmed at d 80 ± 7 after AI. Pregnancy per AI at d 38 ± 3 did not differ among treatments. For cows without a CL at enrollment, there was a tendency toward a treatment effect regarding P/AI at d 38 ± 3 (control 26.1% ± 4.0%; DIB 29.2% ± 4.4%; PRID 38.1% ± 4.8%). Cows treated with an intravaginal P4 releasing device containing 1.55 g P4 had increased P/AI at d 38 ± 3 compared with untreated controls. For cows receiving a P4 device containing 1.0 g P4, there was no difference in P/AI compared with control cows or cows receiving a PRID device. The distribution of VDS at d 8 of the protocol differed among treatments. More cows in the control group had a VDS of 0 (62.0% [199/321]) compared with DIB (1.5% [5/330]) or PRID (2.1% [7/334]) cows. Vaginal discharge had no effect on P/AI at d 38 ± 7 or 80 ± 7 after AI. Pregnancy loss was not affected by VDS. Vaginal pH was affected by VDS at d 8. Vaginal pH differed among the different VDS significantly (VDS 0 = 7.87 ± 0.08; VDS 1 = 7.70 ± 0.02; VDS 2 = 7.18 ± 0.11). Cows without a CL at the beginning of the timed AI protocol benefited the most from supplementing 1.55 g of P4 for 8 d, whereas cows with CL at enrollment had no advantage regarding fertility outcomes.