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.