polledness

Polledness is the hornless phenotype observed in domestic bovids, most notably cattle, and is also reported in goats and sheep. It arises from genetic variation that prevents the development of horns during fetal growth. In cattle, the polled trait is typically governed by a dominant allele at a single locus: animals with at least one polled allele (genotypes PP or Pp) are hornless, while those homozygous for the horned allele (pp) develop horns. The polled gene has been mapped to chromosome 1 in cattle, and different mutations can produce the hornless condition across breeds. In some populations, polled cattle can also exhibit scurs—horn-like growths that are not true horns—due to additional genetic factors; this means that polled status does not always guarantee a completely hornless animal in all genetic backgrounds.

From a management perspective, polledness is highly valued because it reduces or eliminates the need for dehorning, a procedure that carries welfare risks for calves and safety concerns for handlers. Consequently, breeding programs favor the polled allele to improve animal welfare and handling safety while attempting to preserve production traits such as milk yield, growth, and fertility. The spread of polledness has accelerated with genomic selection and marker-assisted breeding, enabling breeders to introduce hornless lines into commercial herds without sacrificing performance.

See also: bovidae, dehorning, animal welfare, genetics of cattle.