254. Effect of donor age and follicle size on oocyte developmental competence in the pig

Abstract

Oocytes utilised for in vitro embryo production (IVP) are typically derived from 3–8 mm ovarian follicles of slaughtered pre-pubertal pigs. Following in vitro maturation (IVM), pre-pubertal oocytes display lower developmental competence (DC) than adult oocytes. The aim of this study was to determine the proportion of follicles 3, 4, and 5–8 mm in diameter on the surface of pre-pubertal and adult ovaries, and assess DC of corresponding oocytes. Oocytes were matured for 46 h in modified medium 199. Mature oocytes from the three follicle size cohorts were activated with calcium ionophore to assess blastocyst embryo formation rate. Data were subjected to arcsine transformation, ANOVA and the Tukey post-hoc test. Compared with adult ovaries, pre-pubertal ovaries contained a higher proportion of 3 mm follicles (46 ± 4 v. 72 ± 4%, P < 0.01), but a lower proportion of 4 mm (33 ± 3 v. 22 ± 3%, P < 0.01) and 5–8 mm follicles (21 ± 5 v. 6 ± 2%, P < 0.01). Adult oocytes from the three follicle sizes displayed similar DC (41 ± 2% to 47 ± 3%). DC of pre-pubertal oocytes improved with increasing follicle size (3 mm < 4 mm < 5–8 mm; 12 ± 4%, 27 ± 8% and 50 ± 8%, respectively; P < 0.05). In conclusion, the predominance of 3 mm follicles accounts for the low DC of oocytes from pre-pubertal donors compared with adult donors. Further research is required to understand DC acquisition in pre-pubertal pig oocytes from the smaller follicles <5mm in diameter.