Relationships between plasma progesterone and 13–14 dihydro-15-keto-prostaglandin F 2α and resumption of ovarian activity during the postpartum period in Brahman cows

Abstract

Blood samples were collected daily from pluriparous Brahman cows (n=23) from a tail vessel beginning on Day 1 after parturition through the third postpartum estrus. Data were analyzed for a period of 21 days after calving as well as for the 7-day period prior to the first postpartum estrus. According to the length of the postpartum interval (period from calving to the first estrus), cows were divided into groups: short postpartum interval, medium postpartum interval and long postpartum interval. Cows were also divided into groups according to corpus luteum function: normal CL short-lived CL and no CL. Daily mean plasma progesterone (ng/ml) declined (P<0.07) from 0.22±0.03 on Day 1 to 0.01±.02 on Day 18. Daily mean PGFM (pg/ml) declined (P<0.01) from 728±78 on Day 1 to 433±78 on Day 5 and continued declining to 112±82 on Day 21. For the 21-day period after parturition, mean PGFM was higher (P<0.01) for short postpartum interval (361±22) than for the medium (259±23) or the long postpartum interval (264±27). During the 7-day period prior to the first estrus, plasma progesterone (P 4) was highest (P<0.02) for cows in the normal CL group followed by short-lived CL and no CL groups. During this 7-day period, plasma PGFM was higher (P<0.01) for cows in the normal CL group than the short-lived CL and no CL groups. Plasma P 4 concentrations in the short-lived CL group began to deoline rapidly on Day 9 after the first estrus. Plasma PGFM concentrations were not different among groups during the first 8 days after the first estrus; however, there was a sharp rise in PGFM concentrations in the short-lived CL group on Day 9 while PGFM concentrations remained low for the normal CL and no CL groups. The decline in P 4 concentrations to baseline levels prior to the second estrus occurred very rapidly in the short-lived CL group; in the normal CL group it occurred in a slower manner. The plasma PGFM peak before the second estrus occurred 5 days before estrus in the normal CL group and only 2 days before estrus in the short-lived CL group. It appears from these results that PGF 2α may be involved in a complex manner in the normal restoration of ovarian activity after parturition in postpartum beef cows.