Mendelian trait/disorder: no

Mode of inheritance: Multifactorial

Considered a defect: no

Key variant known: no

Species-specific description: A very useful summary was provided by Gehrke et al. (2020): "With respect to scurs, the most commonly accepted model of inheritance was initially proposed by White and Ibsen [(1936)] . . . and revised by later studies [Long and Gregory, 1978; Brem et al., 1982] . . . . The model assumes that four biallelic loci interact to control the development of horns: the “symbolic” horn locus (H, which is suggested to be always present and homozygous), the polled locus (with alleles P for polled and p for horns), the scurs locus (Sc for scurs and sc for no scurs) and the African horn locus (Ha for African horns and ha for no African horns) [White and Ibsen, 1936; Long and Gregory, 1978] . . . . Scurs are expected to be masked in otherwise horned animals (p/p), but there is discussion about an epistatic interaction between the polled and scurs loci. However, in the literature contradictory results are reported on the mapping and expression of scurs, and some studies discuss whether the development of scurs depends on sex, the genotype at the polled locus, and heterogeneity at the scurs locus [Capitan et al., 2009; Brenneman et al., 1996; Long and Gregory, 1978; Tetens et al., 2015; Wiedemar et al., 2014] . . . "

Mapping: A tentative locus was mapped to BTA19 by Asai et al. (2002). Since the horns locus is on BTA1, there is now convincing evidence that these two traits are inherited independently in cattle.

Gehrke et al. (2020) reported that "expression of scurs depends on age at phenotyping, sex and polled genotype. Scurs were more prevalent in males than in females. Moreover, homozygous polled animals did not express any pronounced scurs and we found that the Friesian polled allele suppresses the development of scurs more efficiently than the Celtic polled allele. Combined linkage and linkage disequilibrium mapping revealed four genome-wide significant loci that affect the development of scurs, one on BTA5 and three on BTA12. Moreover, suggestive associations were detected on BTA16, 18 and 23. The mixed linear model-based association analysis supports the results of the combined linkage and linkage disequilibrium analysis. None of the mapping approaches provided convincing evidence for a monogenic inheritance of scurs."