Effects of 1 or 2 treatments with prostaglandin F_2α on subclinical endometritis and fertility in lactating dairy cows inseminated by timed artificial insemination

The objectives of the current study were to investigate the efficacy of PGF_2α as a therapy to reduce the prevalence of subclinical endometritis and improve pregnancy per artificial insemination (P/AI) in cows subjected to a timed artificial insemination (AI) program. A total of 1,342 lactating Holstein dairy cows were allocated randomly at 25±3d in milk (DIM) to remain as untreated controls (control, n=454) or to receive a single PGF_2α treatment at 39±3 DIM (1PGF, n=474) or 2 treatments with PGF_2α at 25±3 and 39±3 DIM (2PGF, n=414). All cows were enrolled in the double Ovsynch program at 48±3 DIM and were inseminated at 75±3 DIM. A subset of 357 cows had uterine samples collected for cytological examination at 25±3, 32±3, and 46±3 DIM to determine the percentage of polymorphonuclear leukocytes (PMNL). Subclinical endometritis was defined by the presence of ≥5% PMNL. Vaginal discharge score was evaluated at 25±3 DIM and used to define the prevalence of purulent vaginal discharge. Body condition score was assessed at 25±3 DIM. Pregnancy was diagnosed 32d after AI and reconfirmed 28d later. At 32±3 DIM, the prevalence of subclinical endometritis was reduced by treatment with PGF_2α at 25±3 DIM in 2PGF (control=23.5% vs. 1PGF=28.3% vs. 2PGF=16.7%); however, this benefit disappeared at 46±3 DIM, and 14% of the cows remained with subclinical endometritis. One or 2 treatments with PGF_2α did not influence P/AI on d 32 or 60 after timed AI, which averaged 39.9 and 35.2%. Similarly, treatment with PGF_2α had no effect on pregnancy loss between 32 and 60d of gestation (11.9%). Cows diagnosed with both purulent vaginal discharge and subclinical endometritis had the lowest P/AI and the highest pregnancy loss compared with those diagnosed with only 1 of the 2 diseases or compared with cows having no diagnosis of uterine diseases. Interestingly, subclinical endometritis depressed P/AI and increased pregnancy loss only when it persisted until 46 DIM. On d 32 after AI, cows not diagnosed with subclinical endometritis and those that resolved subclinical endometritis by 46 DIM had greater P/AI than those that remained with subclinical endometritis at 46 DIM (45.4 and 40.0 vs. 25.0%, respectively). Similar to P/AI, cows not diagnosed with subclinical endometritis and those that resolved subclinical endometritis by 46 DIM had less pregnancy loss than those with subclinical endometritis at 46 DIM (9.6 and 13.5 vs. 43.9%, respectively). One or 2 treatments with PGF_2α before initiation of the timed AI program were unable to improve uterine health, P/AI, and maintenance of pregnancy in lactating dairy cows. Cows diagnosed with both purulent vaginal discharge and subclinical endometritis had the greatest depressions in measures of fertility at first AI, particularly when subclinical endometritis persisted in the early postpartum period.