Efficacy of Lidocaine Topical Solution in Reducing Discomfort Reaction of Horses to Intramuscular Vaccination

SIMPLE SUMMARY: Intramuscular injection for vaccination and venipuncture for blood sampling are necessary for routine preventative health care for horses. A considerable proportion of horses react to these procedures, particularly as a needle pierces the skin. Many progress to become “needle shy.” Avoidance behaviors often quickly escalate to dangerous levels. Our clinical experience suggests that topical numbing solutions shown to reduce needle discomfort in other species also help horses better tolerate needles. To critically evaluate this clinical impression, 78 ponies were divided into three groups, each with either 5% or 10% lidocaine solution (commercially available preparations) or 0% control (sterile water) applied two minutes before each of two intramuscular vaccinations. Personnel handling the ponies, performing injections, scoring behavior reactions and analyzing data were unaware of treatment assignments. For both lidocaine treatments, behavioral reactions were lower than control treatment and not significantly different from one another. Fewer than 15% of lidocaine-treated ponies (7 of 51) had greater than a slight flinch reaction, compared to more than half (55%) of control group ponies (15 of 27). This clearly demonstrates that topical anesthetic can effectively reduce the behavior reaction of horses to intramuscular injection, providing convincing support for its routine use to improve animal welfare and care staff safety. ABSTRACT: Vaccinations via intramuscular injection are a key component of preventative health care in horses. Development of problematic behavioral aversion to injections is quite common. Our clinical impression has been that topical anesthetic applied to injection sites can reduce the behavioral reaction; however, this has not been critically tested. To blindly evaluate efficacy, either 5% or 10% topical lidocaine solution or 0% control was applied to injection sites for 78 ponies two minutes before intramuscular vaccination. Mean reaction scores on a scale of 0–3 were 0.84 (se 0.18) for 5% lidocaine solution, 0.62 (se 0.14) for 10% lidocaine solution, compared to 1.30 (se 0.19) for 0% control solution. Reaction scores for both the 5% and 10% lidocaine were significantly lower than for the control group. Additionally, the proportion of subjects with a reaction greater than a slight flinch was 2 of 25 for the 5% lidocaine, 5 of 26 for the 10% lidocaine and 15 of 27 for the 0% lidocaine control. For both the 5% and 10% lidocaine groups, the proportion differed significantly from the control. The difference between the 5% and 10% lidocaine groups was not statistically significant. These findings confirm our clinical impression that application of topical anesthetic just two minutes in advance of intramuscular injection can effectively reduce the behavior reaction of horses.