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Effect of plasma concentrations of progesterone during the first nine days after the IATF conception rates in Nelore cows

Grant number: 11/13427-7
Support type:Scholarships in Brazil - Scientific Initiation
Effective date (Start): September 01, 2011
Effective date (End): July 31, 2012
Field of knowledge:Agronomical Sciences - Animal Husbandry
Principal Investigator:Claudia Maria Bertan Membrive
Grantee:Milene Gondim de Oliveira Alves
Home Institution: Universidade Estadual Paulista (UNESP). Campus Experimental de Dracena. Dracena , SP, Brazil

Abstract

Higher concentrations of progesterone (P4) measured on day 7 after artificial insemination (AI) resulted in an increase in the probability of conception as day 28 post-AI. Experiments carried out independently by different research groups directly or indirectly demonstrated the positive correlation between plasma concentrations of P4 on bovine embryo development and pregnancy rates at the end of the first month of pregnancy. Studies have shown that higher concentrations of P4 on day 5 post-estrus, or P4 supplementation on days 1-4 or 5-9 post-insemination favored embryonic development, induced the secretion of proteins into the uterine fluid and stimulated production t interferon-(Green et al. 2005; Mann and Lamming, 2006). Demetrius et al. (2007) also observed that there was a positive correlation between concentration of P4 at day 7 and probability of conception in cows inseminated after a synchronized estrous cycle. In contrast, this same study, it was observed that the probability of conception of animals that received embryo transfer on day 7 after estrus was not affected by plasma concentrations of P4 measured on the same day. Thus, it is suggested that there is a role developed by P4 in early embryonic development, specifically within the first weeks of pregnancy. The stimulation of preovulatory follicle with eCG results in greater volume of the corpus luteum and progesterone concentration on day 7 after estrus (Baruselli, 2004, Peres 2009), and improve the conception rates of cows (Baruselli, 2004; Peres, 2009; Sa Filho, 2009), supposedly for the beneficial effect of increased plasma concentrations of progesterone observed since the early luteal phase. In this proposal, the objective is to compare the plasma concentrations of P4 in Nelore cows on days 1, 3, 5, 7 and 9 after AIFT in pregnant and non pregnant at 30 days after AIFT, treated or not with hCG equina (eCG) on the day of implant removal. 240 Nellore cows will be used, which have the synchronized estrus by the use of an intravaginal device containing 1 g of progesterone (Cronipress ® - Biogenesis) associated with an injection of 2 mg of estradiol benzoate (Estrogin ® - Farmavet) via intramuscular (IM) . The days of placing the device will be considered the D-10. D-2 in the device is removed and the animals receive an injection of 150¼g of D-cloprostenol (Preloban ® - Intervet). On the day of implant removal (D-2) cows will be divided equally into two groups, not to receive (n = 120) or receive (n = 120) of 400 IU equine chorionic gonadotropin (eCG; Folligon ® - Intervet), via IM at the time of device removal. After 24 hours of implant removal (D-1) females will receive 1 mg of estradiol benzoate (Estrogin ® - Farmavet) via IM. All females will be subject to fixed-time artificial insemination (AIFT) 36 hours after implant removal (D0) with semen andrological within the recommended standards. Blood samples will be collected from all animals on days 1, 3, 5, 7 and 9 after TAI for the plasma concentrations of progesterone are measured by radioimmunoassay technique. The pregnancy diagnosis will be performed by ultrasonography 30 days after AIFT. After the identification of pregnant females, whereas a conception rate to AIFT of about 50%, there will be a comparative analysis of plasma concentrations of P4, where cows are supposed to be divided into four groups: pregnant cows without eCG (pregnant control group, n = 60), non-pregnant cows without eCG (non-pregnant control group, n = 60), pregnant cows with eCG (eCG pregnant group, n = 60) and non-pregnant cows with eCG (ECG Grupo not pregnant, n = 60 ). The hypothesis of this study is that higher plasma concentrations of progesterone are found before the seventh day after AIFT in pregnant or not treated with eCG.