27 Estrus synchronization in the southern white rhino (Ceratotherium simum simum)

B. Durrant; E. Ruggeri; C. Young; N. Ravida; S. Sandmaier; J. VanKempen; J. Capiro

doi:10.1071/RDv37n1Ab27

RESEARCH ARTICLE

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27 Estrus synchronization in the southern white rhino (Ceratotherium simum simum)

B. Durrant ^A , E. Ruggeri ^A , C. Young ^A , N. Ravida ^A , S. Sandmaier ^A , J. VanKempen ^A and J. Capiro ^A

+ Author Affiliations

- Author Affiliations

^A San Diego Zoo Wildlife Alliance, San Diego, CA, USA

Reproduction, Fertility and Development 37, RDv37n1Ab27 https://doi.org/10.1071/RDv37n1Ab27

With the exception of the vulnerable southern white rhinoceros (SWR), all rhinoceros species are endangered, and some face imminent extinction. The preservation of genetic diversity through optimized assisted reproductive technology (ART) is fundamental to the long-term survival of rhinos by maximizing the number of individuals contributing to future generations. In rhinos, ART, including superovulation, ovum pickup (OPU), and in vitro embryo production, is currently moderately successful but may be further improved by synchronizing estrus in oocyte donors before OPU. The effect of estrus synchronization with chlormadinone acetate (CMA, a synthetic progesterone receptor agonist that inhibits follicle growth and maturation by disrupting endogenous gonadotrophin secretion) was examined. Thirty milligrams of CMA was delivered orally daily to seven adult female SWRs. In 15 trials, CMA was administered for 45 (n = 4), 30 (n = 7), or 15 (n = 4) days regardless of the stage of the estrous cycle at the first dose (Table 1). Four individuals participated in more than one trial, with sequential trials separated by at least 4 months to ensure intervening resumption of regular estrous cycling. Fecal progesterone metabolite levels were quantified by RIA and mean values for the week before and the week after CMA treatments were recorded. CMA data were analyzed by one-way ANOVA with Tukey HSD. Follicle growth was assessed by transrectal ultrasound 5–6 days following the last CMA treatment. Progesterone levels for the 30- and 45-day CMA treatments differed significantly. However, by the end of CMA administration, there were no significant differences in progesterone levels for the three treatment groups. The decline in progesterone by the end of all CMA trials regardless of the length of treatment, indicated that even short (15-d) treatment was sufficient to synchronize follicle growth. The initiation of a follicular phase following CMA treatment was confirmed by the growth of multiple small follicles on each ovary of all treated rhinos.

Table 1.CMA treatment and mean progesterone levels.

Mean progesterone (ng g⁻¹)	CMA treatment (days)
Mean progesterone (ng g⁻¹)	15	30	45	P-value
Week before CMA	2084 ± 1583^ab	1748 ± 2506^b	3888 ± 1686^a	0.0321
Week after CMA	1437 ± 143^x	1578 ± 2070^x	672 ± 540^x	0.2557

^a,b,xValues in each row with different superscripts are significantly different.

The authors thank San Diego Zoo Wildlife Alliance’s Wildlife Health and Wildlife Care staffs for their advice, support, and continued collaboration.