Randomized clinical trial to evaluate the efficacy of prostaglandin F2α to treat purulent vaginal discharge in lactating dairy cows

The objectives of this study were (1) assess the effect of purulent vaginal discharge (PVD) on reproductive performance using a 4-point vaginal discharge score (VDS) and (2) to evaluate the effect of PGF(2 alpha) treatment in cows with PVD on reproductive performance. Holstein cows (n = 2,473) from 1 commercial dairy farm had their vaginal discharge scored at 32 +/- 3 d in milk (DIM) using a 4-point scale. Cows were also scored for body condition score and had their ovaries examined using transrectal ultrasound. A VDS-2 or greater was used to define PVD. Cows with PVD were assigned to receive 2 doses of 500 mu g of PGF(2 alpha) analogue (n = 277; Cloprostenol; PGF Veyx forte, Veyx Pharma Ltd., Schwarzenborn, Germany) 14 d apart (odd ear tag number) or remained untreated (n = 272; even ear tag number). All cows not detected in estrus at 90 +/- 3 DIM were enrolled into a timed artificial insemination (AI) protocol. The effect of VDS and the effect of PGF(2 alpha) in cows with PVD on reproductive performance were evaluated separately. First service conception risk (FSCR), time to first AI, and time to pregnancy were used as indicators for reproductive performance. Data were analyzed with Cox's regression and mixed logistic models. The prevalence of PVD was 22.2% (548/2,473). We detected an interaction of parity and VDS for FSCR and time to pregnancy. In primiparous cows, VDS had no effect on FSCR and time to pregnancy. In multiparous cows, VDS had an effect on FSCR and time to pregnancy. Multiparous cows having a VDS-2 or a VDS-3 had decreased odds of pregnancy at first AI compared with cows having a VDS-0. Multiparous cows with VDS-1 or VDS-3 had a decreased hazard of conceiving within 200 DIM. The treatment effect of PGF (2 alpha) was conditional on parity. In primiparous animals with PVD without a corpus luteum present at 32 DIM, treatment with PGF(2 alpha) reduced FSCR. Irrespective of the presence of a corpus luteum, treatment with PGF(2 alpha) decreased the hazard of conceiving within 200 DIM in primiparous cows. Although multiparous cows with PVD treated with PGF(2 alpha) had increased odds of pregnancy at first AI, no treatment effect was observed on the hazard of conceiving within 200 DIM. Our results do not support the blanket use of PGF(2 alpha) as a treatment option in postpartum dairy cows having PVD.