Impact of a novel cytogenetic finding (unusual polyploidy, 50% 2n,XY/50% 3n,XY) on fertility of a cross breed F₃ abondance bull

The present report describes the fertility status of a Cross breed F₃ Abondance bull with a novel cytogenetic finding: 50% 2n, XY/50% 3n,XY chromosomal complement. We report here on a case of a cross breed Baladi x Abondance (F₃ Abondance) male bull with embryos death in vitro and in vivo. A cytogenetic study was undertaken on the chromosomal makeup of cross breed F₃ Abondance bull housed in A.I. Center, Beni-Suef City, Egypt. Blood cultures were made and chromosome spreads were examined, searching for carriers of chromosomal abnormalities. Cytogenetic study showed a high rate of chromosome instability, represented by polyploidy in 50% of the analyzed metaphase spreads.

The fertility of the bull carrying polyploidy was evaluated in vitro and in vivo. Oocytes-cumulus complexes obtained from slaughterhouse-derived ovaries were matured and then fertilized in vitro with frozen/thawed semen from the polyploidy bull and from control bulls with normal karyotype. An assessment was first made of the concentration, vitality and acrosome integrity of the seminal material to be sure that possible differences in the results of the in vitro fertilization experiments were not due to seminal material quality. From the results of the experiment, it can be seen that although the chromosome abnormalities of the bulls did not decrease the fertilizing power of the male gametes, embryo development was impaired in an early phase, around the blastocyst stage (5%) than that of normal bulls (40%) and the non return rate of inseminated cows with spermatozoa from the normal bulls (50%), tested by Chi-square was significantly higher (P<0.05) than that observed in the polyploidy bull (10%).

These data suggest that gametogenesis impairment and decreased spermatozoa fertilizing capacity is responsible for the reduced fertility in bulls with polyploidy. What the data do confirm is that the observed in vivo lowered fertility for abnormal karyotyping bulls is mainly due to early embryonic mortality. Overall, chromosome abnormalities may have a greater influence on male fertility than previously known. Thus, it is important to karyotype subfertile males which serviced cows exhibiting early embryonic death.