Testing in Aril/May will tell you what the the ACTH is during the time of year when it should be at it's lowest. It is good for getting a baseline reading and to monitor whether you may be able to lower pergolide dose during this time vs the dose needed for good control during the seasonal rise period.
Testing in Aug tells you whether the equine is starting it's seasonal rise early or not. If it has started, it gives you a heads up that perg dose needs to start/increase to get/maintain control and prevent other issues from developing (laminitis/founder).
Testing in Oct lets you know where you stand on control during the time of the highest ACTH values. ACTH plateaus, then starts to drop off in normal horses, while PPID ones will tend to top out and maintain that elevated level far longer or may not drop at all.
Part of the answer would depend on why you are using the CTB. If it is to treat known PPID then you would leave the horse on it so you know whether it is doing anything to actually control the disease or not. Stopping the herb/drug would tell you what your values are without any possibly mitigating substances on board. Danger would be if it is controlling any symptoms, those could escalate. Time for withdrawal is unknown but effects of perg are gone in about two weeks so that would seem to be a reasonable time frame.
If CTB was started without any diagnostic testing for PPID then it's murky as you don't know whether there actually is PPID, or whether the CTB is effecting control of PPID, or whether there is early PPID that only shows up during the fall seasonal rise with no current effect from the CTB.
Lavinia, Dante, George Too and Peanut
Jan 05, RI
EC Support Team