Chromosome anomalies in Canadian Guernsey bulls

The performance records of a group of Guernsey bulls used for artificial insemination revealed lower 60 to 90 day non-return rates as compared to that for bulls of the Holstein breed, and nine out of the 19 Guernsey bulls in this group exhibited fertility level below the average for this group. A cytogenetic survey to test whether or not the reduced fertility of these bulls was due to chromosome anomalies revealed a relatively high frequency of chromatid breaks and achromatic gaps in three out of 19 bulls while two carried 59 chromosomes each including a translocation chromosome. The 1/29 translocation heterozygote and the bulls showing achromatic gaps and chromatid breaks were among the five bulls which were consistently below the breed average in fertility as evidenced by the t test (P less than 0.01), whereas the bull with translocation 27/29 (G3) exhibited a non-return rate slightly higher than the breed average (P less than 0.01). It is possible that the chromosomally abnormal bulls contribute to increased returns to service not only because of the defective gametes they themselves might produce but also through their influence on the performance of their daughters.