Associations between polymorphisms of complement component C2 and C9 genes and resistance to mastitis

Mastitis is an infection of the mammary gland that has a huge impact on animal welfare. Due to the high exposure of the udder area to biological and physical factors, dairy cattle are at a high risk of developing the disease, which occurs as a result of intramammary infection with various microorganisms. Not only does bovine mastitis lead to huge financial losses for farmers, which in the long run affects the entire economy, but it also causes suffering to the affected animals. Efforts are therefore being made to minimise the spread of the disease by developing various methods to improve udder health, such as marker-assisted selection (MAS) or genomic selection. The aim of this study was to search for possible associations between polymorphisms of genes encoding complement components C2 and C9 and mastitis resistance expressed as somatic cell count (SCC). The study included a herd of 621 cows of the Polish Black-and-White Holstein-Friesian breed, all kept in the same environmental conditions. Data on daily milk yield, protein and fat concentration, and SCC for all the animals were retrieved from test-day records. Selected polymorphisms were identified by the PCR method. Additive, dominance and epistatic effects between the genes under study were estimated for different lactations, lactation stages and SCC classes. Statistically significant associations were found between the analysed polymorphisms and resistance to mastitis and milk performance traits.