Infections in animal production industries can be reduced through targeted breeding of animals with genetically enhanced disease resistance. This type of breeding should be based on a thorough understanding of host defence and its underlying mechanisms. The genes controlling the omponents of the innate immune system represent a primary target. Their function is highly sensitive to any utational changes in their structure, which has been optimised through long-term evolution. A source of variability is provided by the polymorphism in the genes encoding components of the Toll signalling pathway as one of the main subsystems of innate immunity. The associated set of genes comprises the group of TLR genes encoding the so-called Toll-like receptors (TLRs), as well as genes encoding other key components of the Toll signalling pathway. Specific attention is paid to the genes encoding the crucial interactors of Toll-like receptors, namely the adaptor MyD88 and other adaptors containing the TIR region. Due to the extremely high evolutionary conservation of this region, any structural variation is expected to have functional consequences on the organismal level. The study of the TLR adaptor MyD88, as well as other related adaptors, has been underestimated in farm animal species, as evidenced by the limited number of research outputs. However, this contrasts with the numerous published functional associations for these genes in human medicine. Such a disparity suggests that further research in this direction in farm animal species may yield novel and important findings in the future.