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This study compared the responses shown by lactating dairy cows to four different P4-based protocols for AI at estrus. Cows with no estrous signs 96 h after progesterone intravaginal device (PRID) removal were subjected to fixed-time AI (FTAI), and their data were also included in the study. In Experiment I, follicular/luteal and endometrial dynamics were assessed every 12 h from the beginning of treatment until AI. The estrous response was examined in Experiment II, and fertility was assessed in both experiments. The protocols consisted of a PRID fitted for five days, along with the administration of different combinations of gonadotropin releasing hormone (GnRH), equine chorionic gonadotropin and a single or double dose (24 h apart) of prostaglandin F2α. In Experiment I (40 cows), animals receiving GnRH at the start of treatment showed a significantly higher ovulation rate during the PRID insertion period while estrus was delayed. In Experiment II (351 cows), according to the odds ratios, cows showing luteal activity at the time of treatment were less likely to show estrus than cows with no signs of luteal activity. Treatment affected the estrous response and the interval from PRID removal to estrus but did not affect conception rates 28-34 days post AI. Primiparous cows displayed a better estrous response than multiparous cows. Our findings reveal acceptable results of 5-day P4-based protocols for AI at estrus in high-producing dairy cows. Time from treatment to estrus emerged as a good guide for FTAI after a 5-day P4-based synchronization protocol.

Clomiphene can be used to treat anovulation due to hypothalamus or pituitary gland dysfunction, and it normalizes the luteal phase in stimulated patients. It can be used to estimate ovarian follicle reserve, and may be predictive of ovulation in women aged >/=35 years or with failed IVF. Contraindications include risk of congenital anomalies, chronic liver disease and visual disorders. Clomiphene may impair fertility through its effects on cervical mucus and in causing various endometrial dysfunctions. However, if clomiphene is administered in 50 mg doses, side-effects are avoided and efficacy is similar to that of a 100 mg dose, although daily dosages of 200 mg/day over 5 days can induce ovulation in approximately 70% of treated patients. Gonadotrophin concentrations increase up to days 5-9 when follicles are selected, and clomiphene is effective in patients with polycystic ovary syndrome (PCOS). Fifty percent of normal patients conceive, a value perhaps biased by the antagonistic effects of clomiphene on cervical mucus in some women. Clomiphene is valuable for IVF, and is used by some clinics in combination with HMG or recombinant FSH. Resistance to clomiphene can develop, and human chorionic gonadotrophin may be needed to induce ovulation in clomiphene cycles. Corticosteroids and human menopausal gonadotrophin (HMG) can be combined with clomiphene for stimulation, its combination with HMG long having been a standard protocol in assisted reproduction. PCOS patients may become insulin resistant, a condition improved by the administration of metformin. Other adverse effects include multiple pregnancies, an increase in the rate of multiple births, ovarian hyperstimulation and unsubstantiated claims of ovarian cancer.