Comparison of two closed vitrification methods for vitrifying dromedary camel (Camelus dromedarius) embryos

A total of 184 dromedary camel embryos were vitrified using a novel vitrification kit specifically developed for camel embryos. These embryos were vitrified using a 3-step process by exposing them to vitrification solutions (VS) containing 20% foetal calf serum (FCS) with (+) or without (-) the addition of bovine serum albumin (BSA). Embryos were then further divided into two groups (<or >= 500 mu m), vitrified using a closed vitrification system and stored on a Cryolock (R) embryo storage device or vitrified using solid surface vitrification of the Cryologic Vitrification Method (CVM)(TM) and stored on a Fibreplug (TM) embryo storage device. Embryos were then warmed and transferred in pairs, of approximately equal size, into recipient camels on Day 6 after ovulation. A total of 92 embryos were vitrified using the Cryolock; 86 embryos (C-BSA, n = 46; C + BSA, n = 40) survived warming, and were then transferred into 43 re-cipients. The pregnancy rate (PR) per recipient was 17% (C-BSA: 4/23) and 45% (C + BSA: 9/20) at 20 days after transfer but reduced to 9% and 30% at 60 days of gestation, respectively. For the Fibreplug group, a total of 92 embryos were vitrified, 86 embryos (F-BSA, n = 44; F + BSA, n = 42) survived warming, and were transferred into 43 recipients. The PR per recipient was 73% (F-BSA: 16/22) and 48% (F + BSA: 10/ 21) at 20 days after transfer but reduced to 50% (11/22) and 33% (7/21) at 60 days of gestation, respectively. Of the 39 pregnancies at 20 days after transfer, 77% (30/39) resulted from embryos with a diameter of 300-450 mu m and 23% (9/39) were from embryos with a diameter of 500-850 mu m. In conclusion, 1) significantly higher pregnancy rates were achieved when embryos were vitrified using the Fibreplug than using the Cryolock; 2) the effect of BSA on embryo vitrification is dependent on embryo storage device type and embryo diameter; 3) smaller vitrified embryos (<500 mu m) tend to produce higher pregnancy rates than larger embryos (>= 500 mu m), however, the negative effect of embryo size on embryo vitrification is reduced when embryos are frozen using the original novel vitrification kit (no BSA) solid surface vitrification using the CVM. (C) 2021 Elsevier Inc. All rights reserved.