Q. Over cocktails this weekend, with some local veterinarians and vet tech colleagues, your name came up in regard to a question we had about using a lip twitch. Since it works by releasing endorphins, we were wondering: If the twitch is taken off when the effect seems to be wearing off, how long before it will likely be effective again? One of the local veterinarians remembers that many years ago you and your students studied the endorphin release during twitch application, so you might have the answer to our question. Also, how long after first applying the twitch does it take for the endorphins to reach effective levels, and then how long are the levels effective?

—Jenn Wrigley, CVT, Kennett Square, Pennsylvania

A. What a great question! I can’t imagine many folks converse about lip twitches over cocktails. At first I was bracing for the usual adult horse reproductive behavior gems!

Yes, back in the 1990s we did look at endorphin levels and behavior during a number of activities, including twitch application. We found that there is quite a bit of variation in the intervals, as could be expected. For your first question, for most horses that are not upset, it typically takes just a few minutes of rest after removing the twitch before reapplication can achieve a worthwhile effect. For the few horses we evaluated in a second go-round, after 10 to 15 minutes of rest off the twitch, reapplication resulted in a reasonable rise again in endorphins, along with the corresponding behavior—the droopy lip, glassy eye, and relaxed facial