John's disease and mastitis are two of the most economically important diseases affecting the dairy industry. Interleukin (IL)-12 and IL-23 are two important pro-inflammatory cytokines. The IL-12 receptor (IL-12R) is composed of two subunits; [beta]1 and [beta]2. IL-23 also has a heterodimeric receptor composed of the IL-12R[beta]1 chain and its own unique IL-23R chain. Given the importance of these receptors for regulating inflammation, we hypothesize that variants in the genes coding these receptor domains contribute to variation in the host response to mastitis and enteric 'Mycobacterium avium' subsp. 'paratuberculosis' infection. To test this, a total of 10 single nucleotide polymorphisms (SNP) were identified. No associations were found between these SNP and de-regressed estimated breeding values for SCS. One strong association was found with SNP IL-12R[beta]1 c.81T>C (p = 0.027) and antibody response to MAP infection.