Elevated progesterone concentrations enhance prostaglandin F-2 alpha synthesis in dairy cows

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

The objective was to evaluate the influence of varying plasma progesterone (P-4) concentrations throughout the luteal phase in dairy cows on PGF(2 alpha) production (assessed as plasma concentrations of 13,14-dihydro-15-keto-PGF(2 alpha); PGFM) following treatment with estradiol-17 beta (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 20 mg LH (n = 7), or had ovarian follicles larger than 6 mm 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 3 mg 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 4 h after concentrate feeding. on Day 17, blood was collected from 1 h before to 1 h after a 100 IU OT injection. In Experiment 1, both plasma P-4 and release of PGF(2 alpha) were similar between LH-treated and control cows (P > 0.10). In Experiment 2, plasma P4 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(2 alpha) 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(2 alpha) in response to E-2 or OT. (c) 2008 Elsevier B.V. All rights reserved.