[Monogenic disorders and traits in Swiss suckler cows - A review]

Suckler cow farming is a key part of Swiss beef production, representing extensive farming practices and high standards of animal welfare. Around 7 % of the country's cattle are registered with the relevant breeding association. Switzerland boasts a high degree of genetic diversity, with 38 beef and dual-purpose breeds. This study aimed to systematically catalogue known recessive genetic defects and selected inherited traits of the most common Swiss suckler cow breeds and determine their prevalence. Worldwide, 67 monogenic recessive genetic defects have been identified in beef cattle. Of these, 42 - caused by 45 known gene variants - affect the ten most commonly kept suckler cow breeds in Switzerland. Currently, 40 causative gene variants for 37 genetic defects are routinely tested in Switzerland. No carrier animals have yet been identified for 13 of these variants. In contrast, heterozygous carriers were rarely identified for a total of 27 variants. The breed-specific allele frequencies exceeded 1 % for 14 harmful alleles. The causal variant for retinitis pigmentosa 1 was particularly widespread in Charolais and Angus cattle, as was the causal variant for developmental duplication in Angus cattle. Additionally, single homozygous affected animals were confirmed for the first time in Switzerland: tibial hemimelia in Galloway cattle and progressive ataxia in Charolais cattle. In addition to genetic defects, breeding-relevant monogenic traits such as muscle hypertrophy and hornlessness are also examined. These traits sometimes occur with high allele frequencies in several breeds and can therefore be targeted specifically in breeding programs. SWISScow SNP array genotyping enables harmful recessive alleles to be monitored. Suspected cases should be reported and investigated. Digital breeding planning tools help to avoid risk matings of heterozygous carriers, thereby reducing reproductive losses and improving animal health and welfare in the long term.