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Efficiency of fixed-time artificial insemination in Holstein heifers treated with progesterone intravaginal device associated with GnRH or estradiol benzoate


Estrogen-based protocols for synchronization of ovulation are widely used in Brazil, due to reduced cost and good efficiency in pregnancy rates after fixed time artificial insemination (TAI). However, restrictions on trade in animal products treated with estrogen may limit its use in the future. An alternative to estrogen-base protocols is to replace estrogens by GnRH, in some variations of the well-known "Ovsynch" protocol, widely used in dairy herds of the USA. The purpose of this study is to evaluate the reproductive performance of Holstein heifers submitted to TAI after ovulation synchronization with progestin associated to GnRH (5 day Co-Synch) or estradiol. Holstein heifers will be treated with a vaginal device containing progesterone (DIP) for 5 (Group 1) or 8 (group 2) days. At the time of DIP insert, groups 1 and 2 will receive an intramuscular (IM) injection of GnRH and oestradiol benzoate (EB), respectively. At time of DIP removal, both groups will receive an IM injection of cloprostenol. Seven hours later, half of animals from group 1 will receive a second dose of cloprostenol, while Group 2 will be treated with EB 24 hours later. The animals will be inseminated 72 hours (group 1) or 54 hours (group 2) after DIP removal. Animals from group 1 will receive an IM injection of GnRH at time of AI. Ovarian activity, luteolysis and follicular characteristics will we inferred from plasmatic progesterone concentration and ultrasound exam of ovaries. Pregnancy diagnosis will be performed by ultrasound exam 30 and 60 days after AI. The conception and pregnancy rates will be analyzed by logistic regression, considering variables as ovarian activity, body condition, expression of estrus, ovarian structures (CL and follicle) size, progesterone concentrations and time of the treatments. (AU)

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