Low Incidence of Citrullinemia Carriers Among Dairy Cattle of the United States

Abstract

Bovine citrullinemia is an autosomal recessive disorder that is lethal in the early postnatal period. Dairy bulls from the US were screened for citrullinemia genotype with a mutation-specific assay of semen or leukocyte DNA. One heterozygote was detected among 367 US Holstein bulls tested, corresponding to an incidence of .3%; DNA sequencing showed that this bull (bull C) was heterozygous for the translation-termination mutation described as the cause of bovine citrullinemia. Tests on daughters of bull C revealed that 26 were heterozygous and 25 were homozygous normal, confirming that the condition is autosomal recessive and that bull C was heterozygous. Although bull C was among 273 bulls tested from the top 400 bulls based on Type-Production Index as of July 1990, he was not among the 90 tested from the top 100. He has fewer than 2000 offspring registered with the Holstein Association of America and has few sons in AI. Furthermore, he was culled for other reasons before his citrullinemia status was known. Accordingly, the incidence of citrullinemia carriers is low among US Holsteins, and the impact of the one carrier found on the future of the breed is expected to be minor. No carriers were found among 102 US Guernsey bulls and 53 US Jersey bulls tested. © 1993, American Dairy Science Association. All rights reserved.