Effects of inhibition of prostaglandin F2α biosynthesis during preluteolysis and luteolysis in heifers

Flunixin meglumine (FM; 2.5 mg/kg) was given to heifers at three 8-h intervals, 16 d after ovulation (first treatment = Hour 0) to inhibit the synthesis of prostaglandin F-2 alpha based on plasma concentrations of a PGF metabolite (PGFM). Blood samples were collected at 8-h intervals from 15 to 18 d in a vehicle (control) and FM group (n = 16/group). Hourly samples were collected from Hours -2 to 28 in 10 heifers in each group. Heifers that were in preluteolysis or luteolysis at Hour 0 based on plasma progesterone (P4) concentrations at 8-h intervals were partitioned into subgroups. Concentration of PGFM was reduced (P < 0.05) by FM treatment in each subgroup. For the preluteolytic subgroup, the first decrease (P < 0.05) in P4 concentration after Hour 0 occurred at Hours 24 and 40 in the vehicle and FM groups, respectively. Plasma P4 concentrations 32 and 40 h after the beginning of luteolysis in the luteolytic subgroup were greater (P < 0.05) in the FM group. Concentration at the peak of a PGFM pulse in the FM group was greater (P < 0.05) in the luteolytic than in the preluteolytic subgroup. The peak of a PGFM pulse occurred more frequently (P < 0.001) at the same hour as the peak of an LH fluctuation than at the ending nadir of an LH fluctuation. In conclusion, a reduction in prominence of PGFM pulses during luteolysis delayed completion of luteolysis, and treatment with FM inhibited PGFM production more during preluteolysis than during luteolysis. (C) 2011 Elsevier Inc. All rights reserved.