Behavioral and Physiological Differences in Female Rabbits at Different Stages of the Estrous Cycle

SIMPLE SUMMARY: Estrus involves complex physiological signs and behavioral changes, but the exact ovulation time is difficult to determine, which is very important to improve the fertility of rabbits. This study aimed to analyze female rabbits’ changing behavior and physiology at different stages of the estrous cycle. The female rabbits showed less foraging, drinking, grooming, and biting while in estrus. Related physiological hormones (FSH, LH, P(4), and E(2)) and follicular development at different estrous stages also differed. The number of primary follicles in estrus was significantly higher than in the other stages. Some genes, such as CYP19A1 and IGF1R, related to the estrous cycle in female rabbits were screened via ovarian transcriptome analysis. Overall, extensive information relating the behaviors, hormones, and follicle development in female rabbits at different estrus stages was investigated for appropriate postpartum re-estrus management strategies. ABSTRACT: Estrus involves a series of complex physiological signs and changes in behavior before ovulation, which play a crucial role in animal reproduction. However, there have been few studies that evaluate behaviors during the different stages of estrus cycle in female rabbits. Therefore, more detailed information is needed on distinguishing the various stages of the estrous cycle. This study explored the behavioral and physiological differences at various estrous cycle stages in female New Zealand White rabbits. The continuous recording method was employed to record the daily behaviors of twenty postpartum female rabbits during the estrous cycle. Compared with the diestrus stage, the duration of foraging and drinking behavior in estrus decreased significantly, and the frequency of grooming and biting behaviors increased (p < 0.05). Differences in reproductive hormone levels (FSH, LH, P(4), and E(2)) and follicle development were measured at each stage via ELISA and HE staining. The FSH and LH levels showed an increasing trend and then decreased, with the lowest being in late estrus (p < 0.05). The P(4) level was the lowest in estrus (p < 0.05), and E(2) showed a gradually increasing trend. There was no significant difference in the number of primordial follicles at each stage, but the number of primary follicles in estrus was significantly higher than at the other stages (p < 0.05). To further understand the molecular regulation mechanism of the estrous cycle in female rabbits, we analyzed the ovarian transcription patterns of female rabbits in diestrus (D group) and estrus (E group) employing RNA-seq. A total of 967 differentially expressed genes (DEGs) were screened from the ovaries of female rabbits between the diestrus and estrus groups. A KEGG analysis of DEGs enriched in the estrogen signaling pathway, aldosterone synthesis, and secretion pathway, such as CYP19A1 and IGF1R, was performed. The rabbits’ behavior, related physiological hormones, and molecular regulation also differed at different estrous cycle stages. The results provide recommendations for the adequate management practices of postpartum re-estrus and breeding female rabbits.