Genetic parameters and weighted single-step genome-wide association study for supernumerary teats in Holstein cattle

Area of Science:

• Animal genetics
• Mammalian reproductive biology
• Quantitative genetics

Background:

• Supernumerary teats (SNT) are a common udder abnormality in mammals, negatively impacting milk production, udder health, and animal welfare.
• SNT can lead to economic losses through increased veterinary costs, reduced milk yield, and early culling of affected animals.

Purpose of the Study:

• To investigate the incidence and heritability of SNT in Chinese Holstein cattle.
• To identify genes and genomic regions associated with SNT in this population.
• To explore genetic correlations between SNT and economically important traits.

Main Methods:

• A population of 4,670 Chinese Holstein cattle was analyzed for SNT incidence.
• Heritability was estimated using a threshold model.
• Genetic correlations were calculated between SNT and milk production, body conformation, fertility, health, and longevity traits.
• A single-step Genome-Wide Association Study (GWAS) was performed using 114,485 SNPs.

Main Results:

• The overall incidence of SNT was 9.8%, with an estimated heritability of 0.22.
• Low to moderate genetic correlations were observed between SNT and traits like milk yield and age at first calving.
• GWAS identified 10 candidate genes associated with SNT on BTA4, with the RARRES2 gene highlighted in a region of high genetic variance.

Conclusions:

• SNT is a heritable trait in Chinese Holstein cattle, suggesting potential for genetic selection to reduce its occurrence.
• Identifying SNT-associated genes provides a foundation for marker-assisted selection strategies.
• Understanding the genetic basis of SNT can aid breeders in improving udder health and economic efficiency.