# Genome-Wide Association Study Reveals Single Nucleotide Polymorphisms Associated with Tail Length and Tail Kinks in Piglets

## TL;DR

This study finds that genetic selection for shorter tails in pigs may not be effective due to small genetic effects and associated tail malformations.

## Contribution

The study identifies specific SNPs linked to tail length and kinks in piglets, revealing their limited utility for genetic selection.

## Key findings

- Seven SNPs were associated with tail length in piglets, located on multiple chromosomes.
- Two SNPs on chromosome 2 caused a functional amino acid change.
- Shorter tail genotypes were linked to tail kinks, suggesting negative side effects.

## Abstract

Tail docking is a symptomatic yet effective and widely used, but animal unfriendly, method of reducing the prevalence of tail biting. This led to the idea of genetically shortening tail length through selection. However, this procedure can lead to side effects in the form of tail kinks. The aim of the present study was a genome-wide search for gene markers and candidate genes associated with tail length. The identified marker alleles differed only slightly in their associated tail length. At the same time, the close genetic association between shorter tails and malformations was confirmed. The results of the present study argue against the benefits of genetic selection for shorter tails in pigs.

Tail docking is still used in pigs to reduce the prevalence of tail biting, although it is purely symptomatic and contrary to animal welfare. Genetic selection for shorter tails might, however, help to avoid tail docking and has therefore been proposed. A genetic basis for tail length is known for many species. Variability in tail length, including moderate heritability, has also been demonstrated in pigs. The aim of the present study was to identify genetic markers for tail length and to define candidate genes. To this end, 140 piglets were phenotyped and genotyped at 3 days of age and a genome-wide association study was performed. Seven SNPs were mapped on chromosomes 1, 2, 6, 11, and 15. Two linked SNPs on chromosome 2 resulted in a functional amino acid exchange. The genotypes at the SNPs were only associated with small differences in relative tail length of up to 16.5% (short genotype versus long genotype at SSC15), but at the same time with the occurrence of malformations in the form of tail kinks. The small effect size and the association between tail length and tail kinks, together with the generally pure symptomatic effect on tail biting, argue against the applicability of selection for shorter tails in pigs.