A progesterona (P4) é um dos principais hormônios responsáveis pela ciclicidade reprodutiva e atua na manutenção da gestação em vacas. Esse hormônio caracteriza-se pela rápida metabolização, o que leva a necessidade de disponibilizá-lo de forma lenta a fim de mimetizar sua liberação fisiológica. Diferentes dispositivos de liberação dos progestágenos associados à aplicação de ésteres de estrógeno são utilizados com frequência em protocolos para sincronizar as ondas foliculares e ovulação. Entre os dispositivos liberadores de progestágenos, o mais utilizado é o intravaginal, sendo disponíveis outras alternativas de dispositivos como o auricular, oral, injetável e o adesivo transdérmico. Dessa forma, conhecer as alternativas de implantes de P4 é importante para garantir a eficiência dos protocolos reprodutivos, assim como o bem-estar animal e o desenvolvimento de novos dispositivos de P4. O objetivo dessa revisão é descrever as principais alternativas de implantes de progesterona utilizados na inseminação artificial em tempo fixo (IATF) bem como suas vantagens e desvantagens.

Summary The aim of this study was to evaluate the follicular development, morphological integrity, and oxidative stress of preantral ovarian follicles from Bos taurus indicus females grown in vitro with ascorbic acid. Ovaries (n = 20) from Bos taurus indicus females were collected, fragmented, and were cultured in vitro for 6 or 12 days in minimum essential medium (MEM), or MEM supplemented with 50 or 100 ng/ml ascorbic acid, with an extracellular matrix of agarose gel, in an incubator at 38.5°C; every 2 days, 100% of the culture medium was replaced. The data were analyzed using the chi-squared test and/or Fisher’s exact test. In the event of a significant effect, the proportions were compared using a 2 × 2 proportion test. The oxidative stress analysis data were submitted to analysis of variance followed by the Bonferroni test. Values were considered significant when P ≤ 0.05. The addition of 100 ng/ml of ascorbic acid to the in vitro culture medium of preantral ovarian follicles from bovine females promoted follicular development, was efficient in maintaining morphological integrity, as well as the stability of reactive oxygen species, after 6 days of in vitro culture.

We evaluated the effects of nulliparous, primiparous, and multiparous conditions on the estrus and pregnancy rates in females that did not show estrus but were treated with gonadotropin-releasing hormone (GnRH) at the time of timed artificial insemination (TAI). Nelore females (n = 531) were allocated according to the following categories: nulliparous (n = 144), primiparous (n = 132), and multiparous (n = 255). The animals received a conventional TAI protocol, and estrus expression was identified by the absence of paint in the sacrococcygeal region on the day of TAI. Females that did not show estrus were treated with 10 μg of GnRH together with insemination. The rates of estrus and pregnancy were analyzed using a logistic regression model (P < 0.05). The estrus expression was lower (P = 0.006) in the primiparous (61.36%) group than in the nulliparous (76.39%) and multiparous (75.69%) groups. Similar pregnancy rates were observed in females that showed estrus (nulliparous 84.54%, primiparous 86.42%, and multiparous 80.31%; P = 0.39) and in females that did not show estrus and received GnRH (nulliparous 41.18%, primiparous 56.86%, and multiparous 58.06%; P = 0.24). The total pregnancy rates were also similar (P = 0.98) among the categories (nulliparous 74.3%, primiparous 75.0%, and multiparous 74.9%). The primiparous females had a lower rate of estrus, and the pregnancy rates were similar among the categories that received GnRH.

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The controversial data about antral follicle count (AFC) may be partially explained by the different criteria used to determine what is high, intermediate and low AFC. This study evaluated different classification methods for AFC groups, relating them to the conception rate, dominant follicle size and body condition score (BCS) in cows submitted to timed artificial insemination (TAI). Nelore cows (Bos indicus; n = 935), received a reproductive program consisting of TAI and natural breeding. Conception rate, BCS and dominant follicle size during TAI were evaluated by three AFC methodologies: i) mean and standard deviation: low (≤ 15 follicles); intermediate (≥ 16 to ≤ 44 follicles) or high (≥ 45 follicles); ii) quartiles: low (≤ 15 follicles); intermediate (≥ 16 to ≤ 39 follicles), or high (≥ 40 follicles); and iii) AFC score: I (low; ≤ 15 follicles); II (intermediate; ≥ 16 to ≤ 30 follicles); III (high; ≥ 31 to ≤ 44 follicles) or IV (very high; ≥ 45 follicles).Data were analyzed by a GLIMMIX and Tukey test or binary logistic regression model (P ≤ 0.05). The conception rate to TAI was influenced (P < 0.05) by AFC in the three methods classification, being the highest conception rate observed in the low AFC group regardless of method utilized: Mean (low 61.73% a , intermediate 54.02% ab and high 49.48% b ), Quartiles (low 61.73% a , intermediate 53.59% ab and 51.46% b ) and Score (I 61.73% a , II 54.80% ab , III 53.23% ab and IV 49.48% b ). There were variations (P < 0.05) in the conception rate within the 2.50 to 2.75 BCS range for all AFC classification methods, with the low AFC females presenting the best results, regardless of the method used. Also, females with low AFC showed larger (P < 0.05) diameters of dominant follicles at the TAI regardless of method. The different methodologies used (Mean, Quartile and Score) to AFC classification showed a consistency between the main findings, and we believe that this standardization will facilitate the interpretation of data involving AFC.

Summary The goal of this study was to determine the distribution of preantral follicles in bovine ovaries. Follicular distribution in the ovaries (n = 12) was evaluated in the region of the greater curvature of the ovary (GCO) and the region close to the ovarian pedicle (OP) of Bos taurus indicus heifers of the Nelore breed. Two fragments were obtained from each region of the ovary (GCO and OP). The mean weight of the ovaries was 4.04 ± 0.32 g. The mean antral follicle count (AFC) was 54.58 ± 3.55 follicles (minimum and maximum variation of 30 and 71 follicles, respectively). In total, 1123 follicles were visualized in the region of the GCO; 949 (84.5%) of them were primordial follicles and 174 (15.5%) were developing follicles. The region close to the OP contained 1454 follicles, of which 1266 (87%) were primordial follicles and 44 (12.9%) were developing follicles. The OP region showed a higher proportion of intact follicles in the primordial (P < 0.0001) and primary (P = 0.042) stages compared with the GCO region. The proportion of secondary follicles was similar in the OP and GCO regions. The ovaries of two bovine females (16%; 2/12) contained multi-oocytes follicles, which were characterized as primary follicles. Therefore, the distribution of preantral follicles in the bovine ovary was heterogeneous, with the region close to the OP containing a greater number of preantral follicles compared with the GCO region (P < 0.05).

Melhorar o desempenho reprodutivo é importante para aumentar a lucratividade das propriedades. Assim, nós avaliamos a contagem de folículos antrais (CFA), o escore de condição corporal (ECC), o peso vivo e o comportamento animal sobre à taxa de concepção de vacas Brahman submetidas à inseminação artificial em tempo-fixo (IATF). Vacas (n=122) receberam um protocolo convencional de IATF de três manejos (D0, 8 e 10) a base de estrógeno e progesterona, além do monitoramento da expressão de estro antes da inseminação. O ECC e o comportamento animal foram avaliados em todos os dias do protocolo, o peso foi mensurado no D0 e no diagnóstico de gestação (D40) e a CFA no D0. Para análise, estabeleceu-se os grupos de CFA (baixa, intermediária e alta), do comportamento (calma, inquieta e agitada), do peso (ganhando, mantendo e perdendo) e do ECC (ganhando, mantendo e perdendo). A taxa de concepção geral foi de 50%, e não esteve associada (p>0,05) a classificação da CFA (baixa/52,6%, intermediária/50,9% e alta/45,4%), do peso (ganhando/43,0%, mantendo/54,7% e perdendo/47,1%), do ECC (ganhando/44,0%, mantendo/54,3% e perdendo/37,5%) e do comportamento (calma/43,0%, inquieta/54,7% e agitada/47,1%). No entanto, a baixa CFA apresentou maior (p=0,05) proporção de animais com alta intensidade de estro (94,7%) e foi observado maior escore de reatividade (p=0,001) no primeiro dia de manejo da IATF em relação aos outros dias. Vacas com baixa CFA resultaram em maior proporção de expressão de estro e o primeiro dia de manejo da IATF determinou uma maior reatividade animal em relação aos outros dias do protocolo.   Palavras-chave: Condição Corporal. Inseminação Artificial. Performance Reprodutiva. Peso Vivo.    Abstract Improving reproductive performance is important to increase farm profitability. The  relationship of antral follicle count (AFC), body condition score (BCS), weight, and animal behavior on the conception rate in cows submitted to timed artificial insemination (TAI). Cows (n=122) received a conventional TAI protocol of three managements (D0, 8, and 10) based on estrogen and progesterone, in addition to monitoring estrus expression before insemination. The BCS and behavior score were assessed every day of the TAI protocol. Weight was measured at D0 and in the pregnancy diagnosis (D40), and AFC was determined at D0. For analysis, the groups were established according to AFC (low, intermediate, and high), behavior animal (calm, restless, and agitated), weight variation (gaining, maintaining, and losing), and BCS variation (gaining, maintaining, and losing). The overall conception rate was 50%, and it was not associated with (P>0.05) the AFC classification (low/52.6%, intermediate/50.9%, and high/45.4%), weight variations (gaining/43.0%, maintaining/54.7%, and losing/47.1%), BCS variations (gaining/44.0%, maintaining/54.3%, and losing/37.5%) and animal behavior (calm/43.0%, restless/54.7%, and agitated/47.1%). However, the low AFC showed a higher (P=0.05) proportion of animals with high intensity of estrus expression (94.7%). In addition, a higher score for animal reactivity (P=0.001) was noted on the first day of the management of TAI protocol than to the other days of the hormonal protocol. The low AFC resulted in a higher proportion of cows with high estrus expression and the management practices for TAI determined a greater animals reactivity at the beginning of the breeding program.   Keywords: Body Condition. Artificial Insemination. Reproductive Performance. Live Weight.