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Supernumerary teats (SNT) are any abnormal teats found on a calf in addition to the usual and functional 4 teats. The presence of SNT has also been termed “hyperthelia” since the end of the 19th century. Supernumerary teats can act as an incubator for bacteria, infecting the whole udder, and can interfere with the positioning of the milking machine, and consequently, have economic relevance. Different types of SNT are observed at different positions on the udder. Caudal teats are in the rear, ramal teats are attached to another teat, and intercalary teats are found between 2 regular teats. Not all teats are equally developed; some are completely functional but most are rudimentary and not attached to any mammary gland tissue. Recently, different studies showed the poly/oligogenic character of these malformations in cattle as well as in other mammalian species. The objective of this study was to analyze the genetic architecture and incidence of hyperthelia in Swiss Brown Swiss cattle using both traditional genetic evaluation as well as imputed whole genome sequence variant information. First, phenotypes collected over the last 20 yr were used together with pedigree information for estimation of genetic variance. Second, breeding values of Brown Swiss bulls were estimated applying the BLUP algorithm. The BLUP-EBV were deregressed and used as phenotypes in genome-wide association studies. The gene LGR5 on chromosome 5 was identified as a candidate for the presence of SNT. Using alternative trait coding, genomic regions on chromosome 17 and 20 were also identified as being involved in the development of SNT with their own supernumerary mammary gland tissue. Implementing knowledge gained in this study as a routine application allows a more accurate evaluation of the trait and reduction of SNT prevalence in the Swiss Brown Swiss cattle population.

Supernumerary teats (SNT) are any teats present on a cow`s udder other than the regular four. In Swiss Brown cows, 19.9% carry SNT. Different stages of development of SNT are observed from rudimentary appendices to functional and possibly lactating teats. SNT may promote mastatis, impeach good placement of the milking machine and lower market price of the animals. No genetic analysis of the trais has been done in this cattle population, althought SNT have been routinely recorded with other conformation traits since 1995 in Switzerland. This study aimed to investigate the genetic acrchitecture of this trait through genome-wide association studies (GWAS) performed with imputed whole-genome sequence. Two trait definitions were used: Udder Clearance (UCT) considering whether a cow is carrier of any SNT or has a clear udder and Presence of Supernumerary Mammary Gland (PMG) opposing animal carrier of completely developed and possibly functional SNT with animals with a clear udder or carrier of a rudimentary SNT. Breeding values were estimated for Brown Swiss sires of at least 20 daughters with SNT records using an animal model including the random effects expert-by-year, farm-by-year and animal. The animal's dam life stage—heifer or cow—during its parity was fitted as a fixed effect in the same model. Single SNP regression using deregressed proofs of 1519 bulls with genotypes imputed to the variant list of the 5thRun of the 1000 Bulls Genome Project permitted discovery of three important regions on BTA5, BTA17 and BTA20 associated with the presence or the development of SNT. Regions on BTA17 and BTA20 reached clearly lower p-values (10−7 vs. 10−4) when associated to PMG than UCT, while variants on BTA5 were significantly linked to both trait definitions. No candidate genes on BTA 17 and BTA20 were found after functional analysis. On BTA5, however, the leucine-rich repeat-containing G protein coupled receptor 5 (LGR5) can be considered as the major gene for our trait. Enco