Antibiotic treatments and somatic cell count as phenotype to map QTL for mastitis susceptibility in Holstein cattle breed

Mastitis is one of the most significant diseases affecting dairy cattle profitability. A genome wide association study (GWAS) was performed using the selective genotyping approach to identify Quantitative Trait Loci (QTL) associated with mastitis susceptibility. According to the received antibiotic treatments in all their productive life, 52 lactating cows have been classified in resistant (no therapy and low SCC) and susceptible (more than one treatment and high SCC) to mastitis. Genotyping of animals was performed using the NEOGEN’s GGP Bovine 100K SNP chip and QTL were identified comparing the SNPs allelic frequencies between the two groups. 26 SNPs related to mastitis susceptibility were identified in 9 chromosomes. The use of treatment data, coupled with SCC from milk recording, improved cow’s classification accuracy in resistant and susceptible individuals. For this reason, the mandatory recording of treatments active from January 2022, could be a new source of information to improve the genetic selection for mastitis resistance.