Evaluation of systemic immunologic hyperreactivity after intradermal testing in horses with chronic laminitis.

OBJECTIVE To determine whether systemic immunologic hyperreactivity exists in horses with chronic laminitis, compared with responses for nonlaminitic horses. ANIMALS 7 nonlaminitic horses and 7 CL horses. PROCEDURE In experiment 1, intradermal testing (IDT) was performed on 7 nonlaminitic and 7 CL horses to evaluate the response to a combination of 70 allergens at 15 and 30 minutes and 4 and 24 hours after injection. Three nonlaminitic and 3 CL horses used in experiment 1 were used in experiment 2 to determine whether histologic differences existed between the 2 groups. The H&E-stained tissue sections were evaluated on the basis of 3 criteria. For all analyses, 2-sample t-tests were used to determine significant differences between the groups. RESULTS In experiment 1, CL horses had significantly higher total responses to IDT than nonlaminitic horses at the first 3 time periods. Also, CL horses had significantly fewer total scores of 0 than nonlaminitic horses at all time periods, except at 24 hours. In experiment 2, we did not detect significant differences between groups for any criterion. CONCLUSIONS AND CLINICAL RELEVANCE Results support the hypothesis that CL horses develop hyperreactivity to various antigenic stimuli, compared with responses for nonlaminitic horses. Therefore, the possibility that antigenic challenge may result in exacerbation of clinical signs of laminitis should be discussed with horse owners. Chronic laminitis should also be a consideration when a horse becomes lame following antigenic challenges.