Use of semen from a bull heterozygous for the 1 29 translocation in an IVF program.

In cattle, a translocation of the Robertsonian type between the largest and smallest chromosome leads to a reduction in fertility. This is substantiated by reduced nonreturn rates in daughter groups of bulls carrying the 1 29 translocation and in the heterozygous bulls themselves. This reduction in fertility is thought to be due to the early death of embryos with unbalanced karyotypes. The influence of semen from a bull known to be heterozygous for the 1 29 translocation on the outcome of a bovine IVF program was investigated. There was a significant difference (P<0.005) in terms of cleavage rate (59.8 vs 71.1%) and blastocyst rate (12.0 vs 20.0%) between the carrier and control bull, respectively. There was no difference in blastocyst quality as measured by cell number. The results observed in vitro are consistent with the field fertility records of the 2 bulls in terms of nonreturn rates (59.2 vs 70.6%, for the carrier and control bull, respectively).