Buffering lidocaine heightens aversion to cornual nerve injections in dairy calves

It is best practice to numb the horn buds before disbudding dairy calves, which can be achieved by injecting lidocaine, a local anesthetic, around the cornual nerve. In humans, the acute pain that occurs upon injection of lidocaine can be reduced by neutralizing the pH of the solution with an alkalizing agent, such as sodium bicarbonate. We evaluated whether buffering lidocaine would reduce calves' behavioral and physiological responses to cornual nerve blocks on the left and right side of the head. Female Holstein calves were assigned 1 of 3 treatments: cornual nerve blocks with 5.5 mL of unbuffered lidocaine (n = 9), buffered lidocaine (n = 9), or a sham procedure with no needle inserted (n = 9). Calves that received either type of lidocaine struggled more during the injection than sham calves. However, contrary to our hypothesis, struggling was most marked in calves that received buffered lidocaine. Similarly, calves administered unbuffered or buffered lidocaine had elevated heart rates for 1 or 3 min after the first injection, respectively, compared to the end of the 5-min observation period. Calves in the buffered treatment had lower eye temperatures in the first half of the observation period compared to the second half, consistent with responses cattle show to other aversive procedures, but no changes over time were observed in the other 2 treatments. There were no treatment differences in heart rate variability measures. These results suggest that cornual nerve blocks are aversive, at least in the short term, and that buffering the lidocaine worsens the calf's response to this procedure.Data were collected from the University of California Davis Dairy Facility on 27 calves in 2019. Variables are defined in the README sheet of each of the four Excel files. The R script used to analyze each dataset is provided.See methods in associated publication