Exploring the genetic influences on equine analgesic efficacy through genome-wide association analysis of ranked pain responses.

Multimodal analgesic administration is a promising strategy for mitigating side effects typically associated with analgesia; nevertheless, variation in analgesic effectiveness still poses a considerable safety concern for both horses and veterinarians. Pharmacogenomic studies have started delving into genetic influences on varying drug effectiveness and related side effects. However, current findings have narrow implications and are limited in their ability to individualize analgesic dosages in horses. Hydromorphone and detomidine were administered to a cohort of 48 horses at standardized time intervals, with dosage rates recorded. Analgesic effectiveness was scored (1-3) based on pain response to dura penetration during cerebrospinal fluid centesis. Genome-wide association (GWA) analyses identified two SNVs passing the nominal significance threshold (P < 1 ×10-5) in association with analgesic effectiveness. One SNV identified on chromosome 27 (rs1142378599) is contained within the LOC100630731 disintegrin and metalloproteinase domain-containing protein 5 gene. The second identified SNV is an intergenic variant located on chromosome 29 (rs3430772468) These SNVs accounted for 26.11 % and 31.72 % of explained variation in analgesic effectiveness respectively, with all eight of the horses with the lowest analgesic effectiveness expressing the A/C genotype at rs3430772468, with six of which also expressing the C/T genotype at rs1142872965. Whilst highlighting the multifactorial nature of analgesic efficacy, this study serves as an important step in the application of genome-wide approaches to better understand genetic factors underpinning commonly observed variation in analgesic effectiveness in horses, with the goal of tailoring analgesic dosage to minimize commonly observed side effects and improve the outcomes of equine pain management.