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Improvement of reproductive management protocols based on exogenous hormones to boost the fertility of high-producing dairy cows


In recent years, several changes have been observed in the reproductive physiology of dairy cows, affecting conception rates. These changes are apparently related to high milk production per cow, the result of intense nutritional increment, genetic selection and management techniques aimed at producing milk. Given the direct relationship between the increase in milk production and declining fertility, we have sought alternatives to increase fertility rates. One alternative is the development of protocols for synchronization of ovulation for fixed time artificial insemination (TAI) with the use of exogenous hormones, since the endogenous steroid hormones in high-producing cows are metabolized in a high proportion due to high blood flow through the liver. Thus, this study will involve several experiments in order to, ultimately, develop a TAI protocol that ensures high levels of synchronization of ovulation, as well as an appropriate hormonal environment for optimal oocyte and embryo quality in high producing dairy cows. In Experiment 1 (n = 48), the best dose of estradiol benzoate (EB) concurrently with the insertion of the intravaginal progesterone (P4) device will be determined that more accurately will synchronize the emergence of a new follicular wave; in Experiment 2 (n = 80), we will assess if the protocol associating BE and P4 has the same efficiency of synchronization at different times of the follicular wave, ie, in the presence or absence of a dominant follicle; in Experiment 3 (n = 400), we will evaluate the effect of supplementation of P4 after TAI on the conception rate of lactating cows; in Experiment 4 (n = 600), the effect of P4 supplementation before or simultaneously with the embryo transfer will be tested in lactating cows used as embryo recipients; in Experiment 5 (n = 900), three groups will be compared. G1: cows submitted to conventional AI after estrus observation, G2 cows subjected to TAI after synchronization with estradiol benzoate (EB) and a P4 intravaginal device, and G3: cows subjected to TAI following the same protocol as G2, but with a GnRH injection 3 or 7 days (based on results from Experiment 2) before the start of the protocol, providing high P4 pre AI due to a corpus luteum formed after GnRH. The perspective of this study is that in the end, there will be a substantial increase in knowledge of the factors involved in success or failure of the protocols for TAI, and increased knowledge about reproductive physiology of dairy cows managed under intensive systems in Brazil. It is also hoped that with all this information, we will be able to identify and suggest the reproductive management strategies best suited to different categories of dairy cows or managed under different conditions. (AU)

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Scientific publications (4)
(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)
MELO, L. F.; MONTEIRO, JR., P. L. J.; SURJUS, R. S.; DRUM, J. N.; WILTBANK, M. C.; SARTORI, R.. Progesterone-based fixed-time artificial insemination protocols for dairy cows: Gonadotropin-releasing hormone versus estradiol benzoate at initiation and estradiol cypionate versus estradiol benzoate at the end. JOURNAL OF DAIRY SCIENCE, v. 99, n. 11, p. 9227-9237, . (11/08567-4, 11/11395-0, 11/11344-7)
MONTEIRO, JR., PEDRO L. J.; NASCIMENTO, ANIBAL B.; PONTES, GUILHERME C. S.; FERNANDES, GABRIELA O.; MELO, LEONARDO F.; WILTBANK, MILO C.; SARTORI, ROBERTO. Progesterone supplementation after ovulation: Effects on corpus luteum function and on fertility of dairy cows subjected to AI or ET. Theriogenology, v. 84, n. 7, p. 1215-1224, . (11/11395-0)
MELO, L. F.; MONTEIRO, JR., P. L. J.; OLIVEIRA, L. H.; GUARDIEIRO, M. M.; DRUM, J. N.; WILTBANK, M. C.; SARTORI, R.. Circulating progesterone concentrations in nonlactating Holstein cows during reuse of intravaginal progesterone implants sanitized by autoclave or chemical disinfection. JOURNAL OF DAIRY SCIENCE, v. 101, n. 4, p. 3537-3544, . (11/11395-0)
MONTEIRO, JR., P. L. J.; BORSATO, M.; SILVA, F. L. M.; PRATA, A. B.; WILTBANK, M. C.; SARTORI, R.. Increasing estradiol benzoate, pretreatment with gonadotropin-releasing hormone, and impediments for successful estradiol-based fixed-time artificial insemination protocols in dairy cattle. JOURNAL OF DAIRY SCIENCE, v. 98, n. 6, p. 3826-3839, . (11/11395-0, 11/11344-7)

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