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  • Title: Elevated progesterone concentrations enhance prostaglandin F2alpha synthesis in dairy cows.
    Author: dos Santos RM, Goissis MD, Fantini DA, Bertan CM, Vasconcelos JL, Binelli M.
    Journal: Anim Reprod Sci; 2009 Aug; 114(1-3):62-71. PubMed ID: 19004582.
    Abstract:
    The objective was to evaluate the influence of varying plasma progesterone (P(4)) concentrations throughout the luteal phase in dairy cows on PGF(2alpha) production (assessed as plasma concentrations of 13,14-dihydro-15-keto-PGF(2alpha); PGFM) following treatment with estradiol-17beta (E(2)) or oxytocin (OT). In all experiments, time of ovulations was synchronized with the OvSynch protocol and Day 0 corresponded to day of second GnRH injection. In Experiment 1, non-lactating dairy cows on Day 6 remained non-treated (n=9), received 20mg LH (n=7), or had ovarian follicles larger than 6mm aspirated (n=8). In Experiment 2, cows on Day 6 were untreated (n=9) or received 5000 IU hCG (n=10). In Experiments 1 and 2, all cows received 3mg E(2) on Day 17, and blood samples were collected every 30 min from 2h before to 10h after E(2). Experiment 3 was conducted in two periods, each from Days 0 to 17 of the estrous cycle. At the end of Period 1, animals switched treatments in a crossover arrangement. Animals in Group 2/8 (n=4) received 2 kg/d of concentrate in the first period and 8 kg/d in the second period. Animals in Group 8/2 (n=7) received the alternate sequence. Blood was collected daily for measurement of P(4) 4h after concentrate feeding. On Day 17, blood was collected from 1h before to 1h after a 100 IU OT injection. In Experiment 1, both plasma P(4) and release of PGF(2alpha) were similar between LH-treated and control cows (P>0.10). In Experiment 2, plasma P(4) was elevated to a greater extent on Day 17 in cows treated with hCG (P<0.05) and plasma PGFM was also greater in hCG-treated animals (treatment x time interaction; P<0.05). In Experiment 3, there was a group x period interaction (P<0.01) for plasma P(4), indicating that less concentrate feeding was associated with greater plasma P(4). Release of PGF(2alpha) in response to OT was greater for cows receiving less concentrate (group x period interaction; P<0.05). In conclusion, dairy cows with more elevated blood P(4) concentrations released more PGF(2alpha) in response to E(2) or OT.
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