Context There are contradictory results concerning the relationship between antral follicle count (AFC) and reproductive traits for different breeds of cattle. Understanding this relationship could be useful to selecting animals for breeding. Aims We evaluated the effects of AFC on parameters related to in vitro embryo production (IVP), and the influence of AFC on sexual precocity and conception rate at first fixed timed artificial insemination (FTAI) of Senepol females. Methods Ovarian ultrasound was performed to count antral follicles, and females were classified as low AFC (≤22 follicles), intermediate AFC (23–36 follicles) or high AFC (>36 follicles). Expt 1 evaluated the influence of AFC on IVP, with data from 146 adult cows that were submitted to follicular aspiration. Expt 2 evaluated the influence of AFC on heifer sexual precocity, determined by the presence of a corpus luteum (n = 608), and on conception rate at first FTAI (n = 143). Key results High AFC cows had a greater (P < 0.0001) number of viable oocytes and cleaved embryos and a higher average number of embryos than low AFC cows (38.28 vs 9.92, 38.28 vs 7.75 and 9.34 vs 2.41, respectively). However, the conversion rate (total viable embryos per oocytes) was not affected (P = 0.46) by AFC category. High AFC heifers tended (P = 0.07) to be more sexually precocious than low AFC heifers (16.73% vs 9.47%). An influence of AFC or of AFC category on conception rate at first FTAI was not detected (P = 0.35 and 0.19, respectively). Conclusions Despite greater IVP in high AFC cows, the conversion rate of viable oocytes to IVP was not affected by AFC category. High AFC heifers tended to be more sexually precocious, although AFC did not influence the conception rate at first FTAI. Implications Oocyte quality is probably not influenced by AFC, but selection of animals according to AFC may improve the sexual precocity of the herd.

The aim of this study was to assess whether administration of the gonadotropin-releasing hormone (GnRH) agonist gonadorelin would increase conception rates at 30 (P / ET 30) and 60 (P / ET 60) days of gestation and reduce pregnancy losses (PL) in embryo recipients and what would be the correlation between the animal category and the season of the year in which the embryo transfer would occur. The experiment was conducted on 11 commercial farms in the state of Minas Gerais, Brazil. Recipients were randomly divided into groups: treated (n = 624), cows that received 0.1 mg gonadorelin on the day of FTET, and control (n = 687), untreated cows. All embryos were produced in vitro from oocyte donors of different races. Recipients were classified as heifers, dry cows or lactating cows. Higher conception rate was observed at 30 days (p = 0.03) and 60 days (p = 0.01) in the treated group (45.8%; 43.0%, respectively). Dry and lactating cows had less pregnancy loss (p = 0.001) compared to heifers (2.70% and 2.47% vs 10.42%, respectively). During spring/summer, there was less P/FTET at 30 days (0.024). Embryo transfer carried out in the warmer seasons of the year reduced the pregnancy rate to 60 days and increased pregnancy loss. As an implication, the use of the GnRH analogue can be used as a tool to increase fertility in embryo recipients.

Although studies have shown positive effects of gonadotropin releasing hormone (GnRH) or prostaglandin F 2α (PGF 2α ) at the moment of fixed-time artificial insemination (FTAI) in the conception rate (CR) of cattle, its effects on treatments based on progesterone (P4) and estradiol benzoate (EB) is still not conclusive. The objective of this study was (1) to evaluate the effect of a PGF 2α analogue at FTAI in the CR of crossbred beef cows submitted to a 11d FTAI protocol based on P4 and EB; and (2) to describe the CR between PGF 2α -treated and control cows in different body condition scores (BCS) and parity categories. Crossbred (½ Nellore and ½ Angus) beef cows were submitted to a synchronization protocol and randomly assigned into 2 groups: Control (n = 163), at FTAI cows received 2 mL of saline solution as a placebo, and PGF 2α (n = 163), at FTAI cows were treated with PGF 2α analogue (10 mg of dinoprost tromethamine). Pregnancy diagnosis was performed 33d post-FTAI. Binary logistic regression model was used to analyze the effect of PGF 2α treatment on CR. There was no difference in CR between PGF 2α and control groups (P > 0.05; odds ratio (OR) = 0.92; confidence interval (CI) = 0.59-1.4). A greater CR was found in heifers (P = 0.0006, OR = 2.65, CI = 1.61 -4.38) and multiparous (P = 0.0006, OR = 2.12, CI = 1.04 -4.3) when compared to primiparous cows. Cows with low BCS (4; 9-point scale) showed lower CR when compared with moderate BCS (5-6; 9-point scale) (P < 0.05; OR = 0.10; CI = 0.06 -0.18). There was no numerical difference on CR between PGF 2α -treated and control cows in different BCS and parity categories. The results suggested that the CR in this study was not influenced by 10 mg PGF 2α analogue at FTAI.

À Deus por me abençoar ao longo de toda minha jornada, me protegendo e me dando forças nos momentos difíceis. Aos meus pais (in memoriam), Jair e Sônia, por todo amor, dedicação e educação, e à minha avó Beni (in memoriam), por todo carinho e incentivo. À minha orientadora professora Dra. Ricarda Maria dos Santos pelos ensinamentos, incentivo, apoio e dedicação. Se hoje chego aqui, grande parte de tudo isso tem ela ao meu lado. À toda minha família, tios, tias, irmão, cunhada, sobrinhas, primos e primas, por acreditarem em mim, me apoiarem, por torcerem por mim e por não me deixarem desistir diante das dificuldades. Ao meu namorado Jogbean, por estar ao meu lado sempre me apoiando. Ao professor Dr. José Octávio Jacomini e à professora Dra. Giovanna Faria de Moraes, por fazerem parte da minha banca de mestrado e por todos ensinamentos. À professora Dra. Teresinha Assumpção pelos ensinamentos e por sempre me incentivar a buscar o meu desenvolvimento profissional. Ao Gustavo Vieira e ao Frederico Vieira por disponibilizarem a fazenda com os animais para a pesquisa. E aos funcionários da fazenda por toda ajuda no campo. À toda equipe da Seleção R&S Pecuária Consultoria, e em especial ao Rodrigo Ribeiro Cunha, por me ajudar ao longo de toda a coleta de dados no campo e pelo apoio nesta caminhada. Aos meus amigos por estarem ao meu lado e por me ajudarem sempre que precisei. À todos do Laboratório de Reprodução Animal da FAMEV-UFU, pelos ensinamentos e conselhos. Em especial à doutoranda Mayara Mafra pela atenção e paciência, me ensinando muito no laboratório. Aos colegas da veterinária, que de alguma forma contribuíram para meu enriquecimento profissional. Muito obrigada! "Deus está no controle e a vitória já está garantida, só tenha fé" RESUMO A produção in vitro de embriões (PIVE) e a inseminação artificial (IA) são duas importantes técnicas utilizadas para melhorar o desempenho reprodutivo, a produção e o ganho genético, por isso precisam de atenção para maximizar seus resultados. A contagem de folículos antrais (CFA) é o número de folículos visualizados por ultrassonografia nos ovários. A literatura mostra que utilizando o exame de ultrassonografia é possível classificar as fêmeas bovinas de acordo com o número de folículos antrais, em três grupos diferentes: baixa, intermediária e alta contagem de folículos antrais. Estudos mostram em diferentes raças uma relação entre a CFA e a produção in vitro de embriões e taxa de concepção. Objetivou-se avaliar em fêmeas bovinas da raça Senepol, a relação da contagem de folículo antral com a produção in vitro de embrião, precocidade e taxa de concepção. No experimento 1 foi avaliada a relação entre CFA e ovócitos viáveis, clivados e total de embriões, e no experimento 2, foram avaliadas a relação entre CFA e precocidade (determinada pela presença de corpo lúteo), e entre CFA e taxa de concepção de novilhas. Por exame de ultrassonografia nos ovários, os animais foram avaliados e classificados em CFA baixa (20 ≤ folículos antrais), CFA intermediária (≥ 25 ≤ 45 folículos antrai...