Two experiments will be realized in order to elucidate some questions about the response of luteolytic PGF2a in Nellore cows. EXP I: Three hundred dry Nellore cows will be used in this experiment. Cows will be separated according to age, weight, BCS and parity, in a randomized factorial arrangement (2x4), where we have two ages of CL (7 and 9 day of the estrous cycle), with four different doses of Dinoprost Tromethamine (PGF2a - 12.5, 25, 50 and 2 x 25/8h interval). The treatments follow: 7d12,5 (eg. 7o day of estrus cycle, received 12,5mg de PGF2±), 7d25, 7d50, 7d2x25/8, 9d12.5, 9d25, 9d50 e 9d2x25/8. The cows will be submitted to estrus synchronization and ovulation, which will be determined by ultrasonography (US), and the day of ovulation detection is considered day one. Will be realized 3 experimental periods with 21 days of interval, for reusing without treatment repetitiveness of the same animal. For detection of luteal regression, will be take a blood samples for determination of progesterone concentration at 0, 24, 48 and 72 hours after PGF administration. Estrus detection and distribution will be realized. EXP II: in this experiment will be used 72 dry Nellore cows with confirmation of ovulation after synchronization according program of first experiment. The experimental cows will be separated with a same parameters of EXP I, in a randomized factorial arrangement (3x4). The treatments follow: 5d12.5, 5d25, 5d50, 5d2x25/8h, 7d12.5, 7d25, 7d50, 7d2x25/8h, 9d12.5, 9d25, 9d50, 9d2x25/8h. In the day of PGF treatment, will be realized a biopsy of corpus luteum using a US at 0, 0.5, 24 and 48 hours after PGF treatment. In same time will be take a blood sample for progesterone assay. The CL tissue samples collected will be processed and will be performed a real-time PCR , for the following genes and receptors: StAR, LHCGR, FOS, JUN, PTGS2, PTGFS, PTGFR, IL1B e IL8. In both experiments will be performed the assessment of luteal regression rate, evaluation of the progesterone concentration and the cellular response of CL after PGF injection. To perform the statistical analysis we will be use the statistical program SAS 9.2. using the GLIMMIX approach for the binominal response and MIXED approach for continuous variables.
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