Cryopreservation of immature and mature camel (Camelus dromedarius) oocytes by open pulled straw vitrification

The aim of the present investigation was to establish a reliable vitrification protocol for camel 
oocytes. A total of 540 cumulus oocyte complexes (COCs) were collected by manual slicing and 
divided into two groups. Three hundred oocytes were used to investigate the effect of the open pulled 
straw (OPS) vitrification procedure on the maturation rate of vitrified immature camel oocytes 
compared to control (non-vitrified). The rest (240 oocytes) were employed to evaluate the effect of 
vitrification on the morphological characteristics of immature and mature camel oocytes. COCs 
were treated with  vitrification solution-1 (VS-1) 10% Dimethyl sulfoxide (DMSO) and 10% 
ethylene glycol (EG)  for 30-45 sec and transferred to vitrification solution-2 (VS2)  20% DMSO, 2 
0% EG and 0.5M sucrose . Oocytes were loaded into the OPS and then directly submerged into 
liquid nitrogen (LN2) for 1h. The average value of maturation rate between the vitrified immature 
camel oocytes and the non-vitrified group (control) revealed non-significant differences as indicated 
by expansion of oocytes (88% (132/150), and 85.3% (128/150), respectively). However, the average 
rate of extrusion of the first polar body was significantly reduced in the vitrified immature oocytes 
(20.3%) compared to control group (40.1%).  In addition, the morphological abnormalities occurred 
at higher rate in vitrified immature (GV stage) oocytes than in vitrified mature oocytes 16/99 
(13.6%) vs, 6/106 (6.4%), respectively. Consequently, the survival rate was significantly reduced in 
vitrified immature oocytes compared to vitrified mature oocytes (83.9% vs., 92.4%, respectively).  In 
conclusion, the present study revealed that the camel oocytes could be successfully cryopreserved by 
OPS vitrification using EG and DMSO as cryoprotectant. Moreover, our results demonstrated that 
in camel mature oocytes are more resistant to cryoinjuries than immature oocytes and could 
produce a high percentage of normal oocytes that could be useful for future use in in vitro 
fertilization and camel improvement programs.