The antral follicle count (AFC) represents the number of follicles visualized by ultrasonography in the ovaries. Antral follicle count tends to be variable among cows but with high repeatability within the same individual. In the last decade, AFC has been considered a biological marker of fertility with many positive aspects of reproductive efficiency for those animals with high AFC. For instance, a larger number and better-quality embryos, better pregnancy rates, increased concentrations of circulating progesterone, in addition to other characteristics linked to fertility, are all responses observed in individuals with high compared with those with low AFC in Bos taurus cattle. However, the positive association between AFC and fertility did not follow the same pattern for Bos indicus. Recent articles showed no connection between fertility and number of antral follicles or better reproductive efficiency for high AFC group in Zebu cows. Thus, the aim of this review is to discuss the various data concerning AFC between indicus and taurus cattle. Additionally, we consider AFC to be a possible tool to improve cattle performance in reproductive biotechnology.

Reproductive biotechniques such as embryo production are important tools to increase the reproductive performance in cattle in a short time. In this context, the antral follicle count (AFC), which reflects the population of antral follicles present in an ovary, has been indicated as an important phenotypic characteristic related to female fertility and closely correlated to the performance of in vivo and in vitro embryo production (IVEP). A positive correlation was evidenced between AFC and oocyte retrieval by ovum pick up (OPU) sessions and and with the number of embryos produced. Several studies have reported that females with a high AFC had greater embryo yields compared to those with medium and low AFC. However, controversial results were obtained by studies conducted in different bovine breeds. Many conflicting data may be due to the differences in the experimental design, particularly regarding the classification of animals in AFC groups, subspecies particularities, herd aptitude or even issues related to animal management. Therefore, aspects such as the choice of donor, type of aspirated follicles and the stage of follicular wave need to be clarified. Thus, this text aims to discuss the use of AFC as a reproductive tool and its applications in the in vivo and in vitro production of embryos, besides describing consistent results and new challenges regarding AFC and embryo production.

In the last several years, the high demand for embryo production has resulted in the need to study new methods to make the cryopreservation of bovine embryos produced in vitro more efficient. Despite the advantages offered by in vitro embryo production (IVEP), the major challenge to its greater dissemination is to improve embryonic survival after cryopreservation. Embryos that are produced in vitro are less resistant to cryopreservation compared to those produced in vivo, which is due to the higher accumulation of lipids in their cells, among other factors. In this context, changes in the culture conditions such as the addition of lipolytic chemical substances and the adjustment of fetal calf serum in the medium have been proposed to decrease the lipid amount within the embryos. Several years ago, vitrification allowed good results for in vitro produced (IVP) embryos because of its simplicity, speed and low cost. More recently, another technique applied to simplify the embryo post-thawing rehydration step in vivo, direct transfer (DT), is a strategy that has proven to be of interest in helping to overcome limitations to the cryopreservation of in vitro produced embryos. DT has been performed by commercial laboratories, ensuring good embryo viability after thawing. However, commercial and operational limitations prevent the large-scale use of these techniques. Thus, this review aims to discuss the use of strategies to improve the postcryopreservation survival capacity and the aspects to be overcome so that the cryopreservation of IVP embryos becomes a well-established and commercially applicable technique in addition to presenting new guidelines for embryo transfer (ET) programs from a better selection of recipients.

The productivity in the herds is directly associated with reproduction. Thus, in order to achieve a better efficiency, the most varied reproductive biotechniques have been applied to the plants. Several factors have a direct influence on reproductive performance, including genetics, nutrition, zootechnical management, and sanitation. However, the sanity of the herd through the use of prophylactic measures against infectious agents is often neglected. In this context, particular attention should be paid to health programs, since 37-50% of gestational losses in the herd are consequences of infectious diseases of the reproductive tract caused by viral, bacterial or protozoan agents. Thus, this review will discuss the main advantages obtained with the use of reproductive biotechniques to increase fertility and the epidemiological aspects related to the diseases that cause reproductive failures in cows. Finally, we will also explain the importance of implementing sanitary programs with adequate management and vaccination of animals, to minimize economic losses related to reproductive diseases and, consequently, obtain higher pregnancy rates in the use of reproduction biotechnologies.

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