Follicular Dynamics and Pregnancy Rate in Nellore Heifers Submitted to Fixed-Time Artificial Insemination Protocols (FTAI)

SIMPLE SUMMARY: Reproductive biotechnologies are important strategies to enforce the production of genetically superior animals. The fixed-time artificial insemination is widely used in Brazil and it is especially important in farms located in remote areas, contributing to a better management and increase in genetics and productivity in areas such the Lower Amazon. We evaluated two different protocols of fixed-time insemination using two different hormones in the Nellore heifer raised under tropical conditions. The protocol of the fixed-time artificial insemination using equine chorionic gonadotrophin presented a better outcome in the pregnancy rate compared to the protocol using follicle stimulating hormone. Our tested protocol may be the most suitable alternative to increase conception rates in animals that are raised in an extensive system under tropical conditions in the Amazon. ABSTRACT: This study aimed to evaluate follicular dynamics and pregnancy rates in Nellore heifers submitted to fixed-time artificial insemination (FTAI) protocols associated with equine chorionic gonadotrophin (eCG) or follicle stimulating hormone (FSH). Nellore heifers (n = 259) were used, divided into two studies. Experiment I evaluated the ovarian follicular dynamics in 64 Nellore heifers submitted to different FTAI protocols (n = 32/group) using either FSH or eCG. In Experiment II, the pregnancy rate was evaluated in 195 heifers submitted to FTAI protocols and divided into two groups: FSH (n = 97) and eCG (n = 98). In Experiment I, the ultrasound examination showed that the maximum diameter of the dominant and preovulatory follicles and the ovulation time were similar between the FSH and eCG groups (p > 0.05). However, the ovulation rate was higher in the eCG group when compared to FSH (p = 0.014). In Experiment II, females that received eCG presented a higher pregnancy rate (58.1%) when compared to FSH (40.2%) (p = 0.012). The use of eCG in the FTAI protocol in Nellore heifers promoted a higher ovulation rate and increased pregnancy rate and may be the most suitable alternative to increase conception rates in animals that are raised in an extensive system under tropical conditions in the Amazon.