Abstract The establishment and maintenance of a pregnancy that goes to term is sine qua non for the long-term sustainability of dairy and beef cattle operations. The oocyte plays a critical role in providing the factors necessary for preimplantation embryonic development. Furthermore, the female, or maternal, environment where oocytes and embryos develop is crucial for the establishment and maintenance of a pregnancy to term. During folliculogenesis, the oocyte must sequentially acquire meiotic and developmental competence, which are the results of a series of molecular events preparing the highly specialized gamete to return to totipotency after fertilization. Given that folliculogenesis is a lengthy process in the cow, the occurrence of disease, metabolic imbalances, heat stress, or other adverse events can make it challenging to maintain oocyte quality. Following fertilization, the newly formed embryo must execute a tightly planned program that includes global DNA remodeling, activation of the embryonic genome, and cell fate decisions to form a blastocyst within a few days and cell divisions. The increasing use of assisted reproductive technologies creates an additional layer of complexity to ensure the highest oocyte and embryo quality given that in vitro systems do not faithfully recreate the physiological maternal environment. In this review, we discuss cellular and molecular factors and events known to be crucial for proper oocyte development and maturation, as well as adverse events that may negatively affect the oocyte; and the importance of the uterine environment, including signaling proteins in the maternal-embryonic interactions that ensure proper embryo development. We also discuss the impact of assisted reproductive technologies in oocyte and embryo quality and developmental potential, and considerations when looking into the prospects for developing systems that allow for in vitro gametogenesis as a tool for assisted reproduction in cattle. longterm long operations Furthermore female competence fertilization cow disease imbalances stress remodeling genome divisions review maturation maternalembryonic potential

Abstract Cattle productivity in tropical and subtropical regions can be severely affected by the environment. Reproductive performance, milk and meat production are compromised by the heat stress imposed by the elevated temperature and humidity. The resulting low productivity contributes to reduce the farmer’s income and to increase the methane emissions per unit of animal protein produced and the pressure on land usage. The introduction of highly productive European cattle breeds as well as crossbreeding with local breeds have been adopted as strategies to increase productivity but the positive effects have been limited by the low adaptation of European animals to hot climates and by the reduction of the heterosis effect in the following generations. Gene editing tools allow precise modifications in the animal genome and can be an ally to the cattle industry in tropical and subtropical regions. Alleles associated with production or heat tolerance can be shifted between breeds without the need of crossbreeding. Alongside assisted reproductive biotechnologies and genome selection, gene editing can accelerate the genetic gain of indigenous breeds such as zebu cattle. This review focuses on some of the potential applications of gene editing for cattle farming in tropical and subtropical regions, bringing aspects related to heat stress, milk yield, bull reproduction and methane emissions. environment performance humidity farmers farmer s usage generations selection yield

Resumo: O objetivo deste trabalho foi comparar dois indutores de ovulação - benzoato de estradiol (grupo BE) ou prostaglandina F2α (grupo PG) -, em vacas leiteiras pós-parto submetidas à inseminação artificial em tempo fixo (IATF). Neste estudo, utilizaram-se vacas Girolando lactantes (n=118) com 60 a 120 dias em lactação. Todas as vacas foram tratadas com um implante intravaginal liberador de progesterona (CIDR) associado a 2 mg de benzoato de estradiol (BE) no dia 0. O CIDR foi retirado no dia 9, e todas as vacas receberam 500 µg i.m. de cloprostenol sódico (análogo à prostaglandina F2α). Vinte e quatro horas após a remoção do CIDR, as vacas foram aleatoriamente separadas em dois grupos, que receberam 1 mg de BE i.m. (grupo BE) ou 500 µg de cloprostenol sódico i.m. (grupo PG). As IATF foram realizadas de 52 a 54 horas, em ambos os grupos, após a remoção do CIDR. Não se observaram diferenças nas taxas de ovulação (85,2 vs. 72,7%) e de prenhez (40,7 vs. 38,2%) entre os grupos BE e PG, respectivamente. A fertilidade é semelhante em protocolos de IATF que utilizam prostaglandina F2α ou BE para induzir a ovulação em vacas leiteiras em lactação.

Abstract: The objective of this work was to compare two types of ovulation inducers - estradiol benzoate (EB group) or prostaglandin F2α (PG group) -, in postpartum dairy cows subjected to timed artificial insemination (TAI). Lactating Holstein-Gir crossbred cows (n=118) with 60 to 120 days of milk production were used in this study. All cows were treated with an intravaginal progesterone-releasing device (CIDR) plus 2 mg of estradiol benzoate (EB) on day 0. The CIDR inserts were removed on day 9, and all cows received 500 µg sodium cloprostenol. Twenty-four hours after CIDR removal, cows were randomly assigned into two treatment groups and were given either 1 mg of EB i.m. (EB group) or 500 µg sodium cloprostenol i.m. (PG group). TAI were performed at 52 to 54 hours, in both EB and PG groups, after CIDR removal. No differences were observed in the ovulation (85.2% vs 72.7%) and pregnancy rates (40.7% vs 38.2%) between the EB and PG groups, respectively. Fertility is similar in the TAI protocols that use prostaglandin F2α or EB to induce ovulation in lactating dairy cows.

Objetivou-se investigar os efeitos da ureia na produção, qualidade e estádio de desenvolvimento embrionário e status folicular ao início do tratamento superovulatório de animais alimentados com ureia na dieta. Dezoito cabras da raça Toggenburg foram distribuídas equitativamente para receberem dietas: sem ureia (controle, n=8) e 2,4% de ureia na matéria seca total da dieta (n=10) UMS. Os embriões foram recuperados entre o 7º o 8º dia após o estro pela técnica transcervical e classificados pela qualidade e pelo estádio de desenvolvimento. O status folicular foi determinado por ultrassonografia transretal no dia da aplicação da primeira dose de FSH. O número e a qualidade dos embriões não foram influenciados pela concentração de ureia na dieta. Embriões em estádio avançado de desenvolvimento foram recuperados do tratamento com 2,4% de ureia. A concentração de ureia testada (2,4%) diminui o número de folículos com menos de 5 mm de diâmetro, categoria que se correlaciona positivamente ao número de embriões coletados e ao número e à porcentagem de embriões excelentes e bons.

The effects of feeding urea on embryo production, quality and developmental stages and follicular status at the beginning of a superovulatory treatment of Toggenburg does fed urea diet were investigated in this study. Eighteen females were randomly allocated to receive diets with: no urea (control, n=8), and 2.4% urea dietary dry matter (n=10) UDM. The embryo recovery was performed at day 7 or 8 of estrus cycle by transcervical technique and classified according to quality and developmental stage. The follicular status was determined by transrectal ultrasonography at the first day of FSH injection. The number and quality of embryos were not affected by dietary urea concentration. Embryos from does treated with 2.4% UDM were recovered at advanced stage. Urea concentration (2.4%) decreases the number of follicles with less than 5 mm diameter. This follicle class is positively correlated to the number of recovered embryos and to the number and percentage of excellent and good embryos.