Blood levels of the prostaglandin F2 alpha metabolite during the postpartum period in Bos indicus cows in the humid tropics.

Plasma levels of the prostaglandin F2 alpha metabolite (15-ketodihydroprostaglandin F2 alpha) were determined by radioimmunoassay in 26 postpartum multiparous Brahman cows. Variation in the concentrations of the metabolite was high among animals. 15-Ketodihydro-PGF2 alpha concentrations on day 0, 5, 10, 15 and 20 postpartum ranged from 402 to > or = 1000, from 251 to > or = 1000, from 237 to > or = 1000, from 75 to 608 and from 75 to 267 pmol l-1, respectively. The prostaglandin metabolite levels were elevated at parturition and remained elevated thereafter for periods varying up to 10 to 23 days postpartum (16.7 +/- 0.7 days, mean +/- SEM). Uterine involution (UI) was completed by 28.0 +/- 0.8 days (ranging from 20 to 36 days). A markedly linear decrease of 15-ketodihydro-PGF2 alpha levels (P < 0.001) occurred from parturition until Day 23 postpartum. A significant correlation between the duration of the elevated PGF2 alpha metabolite and the time required for completion of UI was observed (r = -0.05, P < 0.01). The effect of parity (PT) on 15-ketodihydro-PGF2 alpha levels was not significant, however the relationship between UI and PT was affected (r = -0.59, P < 0.001). Both PGF2 alpha release and PT had effects on the variability of UI (R2 = 0.62, P < 0.001). No significant relationship was found between elevated levels of 15-ketodihydro-PGF2 alpha UI and PT with postpartum anoestrous interval (PPAI).