Cryopreservability of caprine oocytes and embryos by conventional straw and open pulled straw vitrification
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Date
2006
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Department of Animal Reproduction, Gynaecology and Obstetrics, College of Veterinary and Animal Sciences, Mannuthy
Abstract
Objective of the study was to compare the cryopreservability of caprine oocytes and embryos by Conventional Straw (CS) and Open Pulled Straw (OPS) vitrification.
Oocytes retrieved by slicing the abattoir origin ovaries of Malabari goats/ its cross bred, having at least one complete layer of cumulus cells were randomly assigned for CS and OPS vitrification procedure. After thawing and cryoprotectant removal oocytes were examined again for morphological viability and membrane integrity by FDA staining.
The total recovery of good quality oocytes from 73 ovaries and its average yield per ovary were 206 and 2.82 respectively. Out of this 85 and 54 oocytes respectively were subjected to CS and OPS vitrification.
The percentage recovery of morphologically viable oocytes after thawing was higher for OPS than CS vitrification (70.59 vs. 42.11). The higher recovery rate of oocytes for OPS over CS vitrification indicated the superiority of the technique in maintaining the morphological viability of oocytes. Only 3.92 per cent of the OPS vitrified thawed oocytes showed ZP damage, which was lower than that after CS vitrification (5.25). Higher cumulus damage observed after CS than OPS vitrification (36.8 vs. 11.7 %) indicated the higher efficiency of OPS in reducing the osmotic damage of cumulus cells. A higher percentage of oocytes (52.9) were recorded as FDA viable after OPS than CS vitrification (31.58).
The vitrification efficiency of caprine embryos were studied using embryos obtained from fresh and repeatedly superovulated adult Malabari goats. Superovulation was achieved with 133 mg pFSH after synchronization using 1.5 mg norgestomet and 10 mg of prostaglandin. Thirty four transferable quality embryos were equally divided and subjected to vitrification by CS and OPS methods. After a storage period of minimum 10 days the vitrified embryos were examined for morphological characteristics and membrane integrity by FDA staining.
The response to synchronization was hundred per cent in fresh and repeatedly superovulated groups. The average number of anovulatory follicles observed in fresh and repeatedly superovulated goat was 7.17 ± 2.0 and 5.17 ± 1.08 respectively. Average number of ovulation in fresh goat (18.5 ± 2.19) was higher than that of repeatedly superovulated goat (11 ± 2.74). Significantly higher (P<0.05) average recovery of embryos was noted in fresh animal (9.33 ± 3.4) than in repeatedly superovulated animal (0.67 ± 0.49). Adhesion of reproductive tract due to earlier surgical handling led to lower recovery of embryos from repeatedly superovulated goats.
Embryo recovery rate after OPS was higher than CS vitrification (100 % vs. 82.35 %). Similarly the recovery rate of morphologically viable embryos was also higher for OPS (88.24 %) than CS vitrification (50 %). After CS vitrification, 14.28 per cent of the vitrified embryos showed ZP damage while none of the embryos subjected to OPS vitrification showed similar damage. After FDA staining a higher percentage (76.47) of OPS vitrified embryos retained membrane integrity of blastomeres than CS vitrified embryos (28.57).
Present study indicated that OPS is a far superior technique than CS vitrification for cryopreservation of caprine oocytes and embryos. Presence of morphologically viable non-fluorescein oocytes and embryos with FDA staining inferred that viability assessment of oocyte and embryo based on morphological characteristics alone is not enough, but it should be coupled with other non-invasive technique such as FDA staining. The study further revealed that the embryo yielding efficiency of fresh animal was significantly higher than repeatedly superovulated animals.
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