Ovarian ultrasound analysis for developing temporal and spatially explicit hormone regimens for induced ovulation and egg deposition in the tiger salamander (Ambystoma tigrinum)

Authors: MARCEC-GREAVES, RUTH - Mississippi State University; VANCE, CARRIE - Mississippi State University; WILLARD, SCOTT - Mississippi State University; KOUBA, ANDREW - Mississippi State University

Submitted to: Theriogenology Wild
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/6/2023
Publication Date: 6/7/2023
Citation: Marcec-Greaves, R., Vance, C.K., Willard, S.T., Kouba, A.J. 2023. Ovarian ultrasound analysis for developing temporal and spatially explicit hormone regimens for induced ovulation and egg deposition in the tiger salamander (Ambystoma tigrinum). Theriogenology Wild. 277:100038-46. https://doi.org/10.1016/j.biocon.2022.109850.
DOI: https://doi.org/10.1016/j.biocon.2022.109850

Interpretive Summary: This study develops new knowledge regarding female caudate reproductive biology, especially related to tiger salamander oogenesis and follicle maturation. Using ultrasound to tailor temporal and spatially explicit exogenous hormone regimens for supporting reproduction in caudates is beneficial for long-term genetic management, sustainability of CBPs and producing animals for reintroduction and recovery efforts. Moreover, the use of ultrasonography can potentially impact the welfare of caudates in these CBPs. For example, managers can use ultrasonography to assess a female salamander’s follicular and oocyte development stage and make informed decisions on whether they should be treated with hormones or scale the protocol to an individual’s follicular status, thereby reducing the number of hormone administrations. Thus, there are clear benefits for the long-term health and physiology of the animals by reducing different aspects of stress the salamanders would experience during the various ART procedures.

Technical Abstract: Conservation breeding programs (CBPs) for threatened salamander species depend on reliable reproduction. We followed ovarian maturation and oviposition in eastern tiger salamander (Ambystoma tigrinum) females treated with exogenous hormone regimens developed within a framework of grading their initial follicular stages based on oocyte size and echogenicity (G0 = little/no development; G1 = minor development; G2 = moderate development; G3 = extensive development). The exogenous hormones used in this study included human chorionic gonadotropin (hCG) and gonadotropin releasing hormone (GnRH), where lower concentrations of hCG were used as a priming hormone compared to the ovulatory dose, which included both hCG and GnRH. The three hormone treatment regimens consisted of: (1) an extended prime plus ovulatory dose; (2) a short prime plus an ovulatory dose; and (3) an ovulatory dose only. The three exogenous hormone regimens were trialed for optimal spawning success based on ovarian ultrasound grades 1–3, in which higher doses of priming hormones were administered to salamanders with less developed follicles to stimulate oogenesis, prior to a final ovulatory dose. The three exogenous hormone regimens and three ovarian grades were used in a 3 × 3 factorial design, with n = 6 females for each factorial combination, and efficacy assessed by ovarian grade and/or exogenous hormone regimen on proportion of animals laying eggs, egg numbers, and latency to egg deposition. The salamanders in the most advanced initial stage of follicular development (G3) were most likely to ovulate and lay eggs and those with low follicular development (G1) the least likely. Initial follicular stages also affected the egg numbers, with G3 females laying the most eggs and G1 laying the fewest. Moreover, we found a significant interaction effect of exogenous hormone treatment and ovarian grade, in which G1 females required the greatest numbers and levels of exogenous hormone doses to induce oviposition and G3 the least. These findings show that ultrasound can be used with Ambystomid species to develop optimal spatial and temporal hormone regimens for ovulation and oviposition, depending on follicular maturation, thereby enhancing the efficiency of CBPs, improving animal welfare, and advancing genetic diversity management.