CYTOGENETIC EVALUATION OF OVA FROM PUBERTAL AND 3RD-ESTROUS GILTS

Cytogenetic characteristics of ova surgically recovered from 19 first-estrous (pubertal) gilts were compared with those from 24 third-estrous gilts. Mean percentage recovery of ova was 82.1 +/- 2.9%. A total of 159 and 203 ova from first- and third-estrous gilts, respectively, were evaluated. Gilts at first and third estrus ovulated more mature ova (metaphase I-II chromosomes visible) than immature ova (germinal vesicle stage through prometaphase stage), but the percentage of immature ova in gilts at first estrus was greater than in those at third estrus (33.1 vs. 24.1%, p < 0.06). Percentage of mature ova with a normal haploid complement of chromosomes was similar in gilts at first and at third estrus (52.7 vs. 47.5%, p > 0. 10). Percentage of hyperploid ova did not differ between first- and third-estrous gilts (10.8 vs. 5.9%, respectively); however, estimated frequency of nondisjunction appeared greater for gilts at first than at third estrus (21.6 vs. 11.9%, p < 0. 10). These data suggest that ova of first-estrous gilts are inferior in quality compared to those of cyclic gilts.