Microscopic Morphology and Apoptosis of Ovarian Tissue after Cryopreservation using a Vitrification Method in Post-Hatching Turkey Poults, Meleagris gallopavo

The objectives of this study were to examine morphological changes of oogonia and primordial follicles in the ovaries of turkey poults within the first week after hatching, and to evaluate the effect of cryopreservation on histology and apoptosis of these immature ovaries. Ovaries from poults at Day 1, Day 3, Day 5 and Day 7 post-hatch were cryopreserved using a modified vitrification method. The histology of oogonia and primordial follicles in fresh and cryopreserved tissue was assessed, and the apoptosis of tissue in different age groups was identified using a terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. The mean oogonium diameter in fresh tissue increased from 11.9±1.3 µm (Day 1) to 15.2±2.7 µm (Day 7) within the first week; however, oogonia in cryopreserved tissue from Day 3 and Day 7 ovaries were smaller than those in fresh tissue (P<0.05). Formation of primordial follicles was observed as early as Day 5. For Day 7 ovaries, follicles in cryopreserved tissue were smaller than those in fresh tissue; this was also true for oocyte diameter (P<0.05). Apoptosis was most frequent in Day 1 fresh tissue, which was reduced as the poults aged. The frequency of apoptosis in cryopreserved tissue was comparable among age groups. This study provides the first documentation of morphological changes in the turkey ovary within the first week post-hatching. Results suggest that oogonia and primordial follicles that are smaller in size could be more resistant to the damage caused by cryopreservation. Of the ages assessed in this study, it is concluded that 3 days of age appears optimal for recovery of donor ovaries for cryopreservation, taking the advance of reduced cryoinjury and ease of tissue handling at this age.