**5. Risk factors for mastitis**

There are host-, pathogen-, and environmental-related risk factors that predispose dairy cows to mastitis. The host risk factors include age (parity), stage of lactation, somatic cell count, breed, the anatomy of the mammary glands/morphology of udder and teat (diameter of teat canal and conformation of the udder), and immune competence (immunity) [153] (**Figure 1**). The environmental risk factors include the proper functioning status of milking machine, udder trauma, sanitation, climate, nutrition, management, season, and housing condition [154]

**Figure 1.**

*Risk factors for mastitis. SA, Staphylococcus aureus; EC, Escherichia coli; SU, Streptococcus uberis; SCC, somatic cell count; AMR, antimicrobial resistance.*

(**Figure 1**). The pathogen risk factors include type (bacteria, fungi, yeast, and algae), number (large number and small number), virulence (highly, moderate, or less virulent), frequency of exposure (dirty farm floor, dirty milking machine, and dirty teat drying towels frequently expose to pathogen; clean floor, clean milking machine, and clean teat drying towels less exposure to pathogens), ability to resist flushing out of the glands by milk (ability to adhere or attach to and invade or internalize into mammary epithelial cells), zoonotic (transmit from cow to human or vice versa) potential, and resistance to antimicrobials [4] (**Figure 1**). The warm, humid, and moist climate favors the growth of bacteria and increases the chances of intramammary infection (IMI) and mastitis development [154]. The incidence of mastitis varies from farm to farm due to the combined effects of these different factors that increase the risk of disease development.

Dairy cows are highly susceptible to IMI during the early dry period due to increased colonization of teat skin with bacteria. Bacterial colonization of teat increases during the early dry period because of an absence of hygienic milking practices including pre-milking washing and drying of teats [155], as well as preand post-milking teat dipping in antiseptic solutions [156, 157] that are known to reduce teat end colonization and infection. An udder infected during the early dry period usually manifests clinical mastitis during the transition period because of increased production of parturition inducing immunosuppressive hormones [158, 159], negative energy balance [160], and physical stress during calving [161].
