We certainly wish that there could be guaranteed improvement. In my experience, almost every animal has had positive effects as a result of acupuncture. However, not all animals have tolerated being handled (much less allowing the needles to be placed effectively) — these are the exceptions. Most tolerate the treatment well. And now I can often use the Infrared Stimulator for these patients.
There have been a few animals who’s disease state is so advanced, or are on such overwhelming medications, that they have not been able to respond reasonably. And perhaps the biggest block to improvement can be owner frustration — it is not always a fast way to see response!
As for how long to effect — this really depends on how severe and long standing the problem is with your pet, what factors (such as medications and external influences) might interfere with the assessment and/or treatment, and the diagnostic and treatment skills of the acupuncturist [me — I wish I were perfect and knew everything]. Some patients have seen excellent response with only one treatment. Others have taken 10-12 treatments to see a reasonable response.
And of course there are some patients that do not respond as well as we would like. Sometimes I will recommend Chiropractic treatments, and for some this seems to help and be synergistic with the acupuncture, and for others I might suggest Homeopathy, massage, hydrotherapy, etc., or conventional medicine, either concurrently or instead of acupuncture and/or herbs (see below), depending on the situation and concerns.