Are scurs in heterozygous polled (Pp) cattle a complex quantitative trait?

Area of Science:

• Animal Genetics
• Molecular Biology
• Livestock Breeding

Background:

• Polled (hornless) cattle breeding offers welfare benefits over calf dehorning.
• The genetic basis of horn and scur development in cattle remains poorly understood.
• Scurs are unexpected horn-like growths in polled cattle, necessitating further genetic investigation.

Purpose of the Study:

• To investigate the genetic factors influencing polledness and scur development in Holstein-Friesian cattle.
• To describe the phenotypic heterogeneity of scurs in relation to polled genotypes.
• To identify genetic loci associated with scur formation.

Main Methods:

• Phenotypic examination and direct gene testing for polledness in 885 Holstein-Friesian cattle.
• High-density genotype data analysis in 232 animals using association and linkage mapping.
• Exploratory data analysis to assess scur expression factors like age, sex, and genotype.

Main Results:

• Scur prevalence is influenced by age, sex, and polled genotype, with males showing higher prevalence.
• The Friesian polled allele is more effective at suppressing scurs than the Celtic polled allele.
• Four significant loci (BTA5, BTA12) and suggestive associations (BTA16, 18, 23) for scurs were identified, refuting simple monogenic inheritance.

Conclusions:

• The study challenges the traditional monogenic model for horn and scur inheritance.
• An oligogenetic model is proposed to better explain the complex inheritance of polledness and scurs in cattle.