Factors affecting in vitro oocyte maturation in Southern white rhinoceros (Ceratotherium simum simum)

Abstract

BACKGROUND : Population numbers of free-roaming rhinoceros are dwindling while natural breeding in captive populations is challenged by sub-optimal fertility. When natural breeding programmes fail and population numbers continue to decline, the use of assisted reproduction technologies (ART) as a conservation tool to save wildlife species from extinction is imperative. Assisted breeding programmes in rhinoceros are challenging and attempts to develop species-specific ART beyond artificial insemination have been limited. This study evaluates various ex- and in-situ factors that could potentially affect in vitro oocyte maturation (IVM) in the Southern white rhinoceros (SWR). OBJECTIVES : To identify predictors of oocyte maturation following ovum pick-up (OPU) procedures performed on a large number of rhinoceros under different management conditions. METHODS : Data from 85 OPU procedures between November 2018 and June 2023 were obtained for this study. A total of 23 factors (three animal, four environmental, 16 laboratory) were evaluated as potentially affecting IVM success. RESULTS : Of the 85 procedures performed on 59 SWR, a total of 265 oocytes were collected with a median of two oocytes (range 0–18) per OPU. Eighteen (18) of the procedures yielded 0 oocytes. The overall maturation rate was 30% (80/265), and six identified factors had significant univariate associations with maturation outcome, of which three remained in the multivariable model. CONCLUSION : Farming system, season and oocyte density in maturation medium (> 100 ul/oocyte) were independently associated with improved maturation success (p < 0.05).