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The main function of the corpus luteum (CL) is progesterone (P4) production, a factor which regulates the estrous cycle and provides proper embryo and fetus development, the hormone that determines the efficiency of reproduction. Estrus synchronization is one of the basal methods applied in reproductive biotechnics. However, pharmacological manipulation of the estrous cycle may cause various CL dysfunctions, including abnormal P4 synthesis after superovulation or synchronization of the cycle. In the authors studies the influence of different methods of estrous synchronization (injection of PGF₂α analogues: dinoprost, cloprostenol and luprositiol; or gestagens treatment: norgestomet) on CL sensitivity to luteotropic factors (LH and PGE₂) was investigated. With the use of PGF₂α analogues the lower action of luteotropic factors on the CL function was demonstrated in the CL after estrus synchronization. Physiological CL sensitivity to the stimulation was observed in CL from the cows with norgestomet-synchronized cycles. The only effects of dinoprost on CL functioning in vitro were conferrable and similar to the natural PGF₂α action. Other PGF₂α analogues much more powerfully and differently influenced the cells/tissues of the bovine reproductive tract compared to natural PGF₂α action. Lower P4 production in the CL after hormonal manipulation may cause insufficient protection of the embryo by the CL products during the first critical pregnancy period and lead to the early termination of pregnancy.
The aim of the study was to establish the possibility of inducing estrus in Leine ewes apart from the reproduction period by means of gestagene (Chronogest-Intervet) and a double injection of PMSG (Gonadotropin-Biovet) at priming - 50 iu and stimulating - 500 iu doses, and to compare the effects of estrus synchronization with the method used until now in which one injection of PMSG was applied. The efficacy of estrus synchronization confirmed by lambing in the group in which priming was used was 55.9%, and in the group in which only one stimulating dose of PMSG was applied was 58.3%. It can be assumed that the use of small priming dose of PMSG during estrus synchronization did not affect the efficacy of estrus synchronization and ovulation. In the group with implanted gestagene, only 8% of ewes lambed, indicating a very strong relationship of reproduction period with the season in Leine sheep. Out of season, the lambing period effectively changed without PMSG stimulation. For a preliminary evaluation of the efficacy of estrus synchronization and lambing the determination of the level of progesterone appeared to be useful mainly to confirm lambing (85.8-89.6% concordance).
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