287 RESCUE AND IN VITRO MATURATION OF FOLLICULAR OOCYTES IN CHINCHILLA LANIGER

Abstract

The chinchilla is a hystricomorph rodent with a natural habitat in the Andes mountains of Chile (see review by Boussarie 2002 Proc. 27th WSAVA Congr.). For most of the chinchilla subspecies, the decline in the natural population can be attributed to human destruction of the native ecosystems and hunting for fur. Chinchillas are listed as a protected endangered species, at immediate risk of extinction. In Europe, chinchillas are reared for pets and fur production. The female has a seasonal polyestrous reproductive activity with a breeding season from November to May. The estrous cycle length is variable (28–41 days), with an estrous duration of 2 days. After a gestation of about 112 days, a litter of 1 to 6 young is born (see reviews by Morrow 1986 in Current Therapy in Theriogenology 2, W.B. Saunders; and Collot 1998 in Proc. I EVSSAR Congr.). Reproductive biotechniques in this species could play an important role in managing both captive and natural populations as well as in sustaining and improving genetic and global biodiversity. The specific aim of this preliminary work was to standardize an efficient in vitro maturation (IVM) procedure for Chinchilla laniger oocytes so that it will be possible, in the future, to perform IVF and embryo cryopreservation and transfer. Oocytes from 4 cyclic breeding females were recovered by slicing ovaries, obtained by ovariohysterectomy, and were matured in vitro according to the procedure described for bovine oocytes by Dell'Aquila et al. (2002 Mol. Reprod. Dev. 63, 210–222). Two trials of 2 estrous subjects each were performed, on the basis of behavioral signs of estrous and vaginal cytology (Harris-Schorr staining), in the early and late breeding seasons. During estrus, the vaginal smear consisted of superficial cells, further neutrophils, and small and large intermediates, whereas parabasal cells were not found. At the end of the culture time, oocytes were stained with Hoechst 33258 and evaluated for the stage of meiotic maturation. Three out of 4 oocytes recovered in November (75%) reached full meiotic maturation, showing the second metaphase plate and the first polar body (PB) extruded. The fourth oocyte, showing the first PB together with multiple pronuclear structures, was classified as activated. On the contrary, none out of 12 oocytes recovered in May reached full maturation. Of them, 7 (58%) remained at the germinal vesicle stage, 2 (17%) reached metaphase I, and 3 (25%) showed abnormally dispersed chromatin configuration. To our knowledge, this is the first study reporting that chinchilla oocytes can be matured in vitro by bovine IVM procedures. Even though the number of oocytes was poor, we can hypothesize that oocytes from C. laniger are best collected in the breeding season when subjected to an IVM technique.