My mare has been in regular work for over a year and is doing low level dressage. She tested positive for PSSM but to my knowledge has never tied up. She is being fed PSSM high fat diet. She is reluctant to 'march' energetically when I first get on her, but at about 20 minutes into the ride a switch goes off and her energy increases. Is this common in EPSM/PSSM horses or is this a training issue that I must push past? My trainer insists that she marches immediately when I ask her to. Is this also symptomatic of not getting enough fat in her diet?
Thanks so much.

The first thing to do is to calculate how much fat she is getting in her diet. Two cups of oil has 1 pound of fat. You can calculate fat from high fat feeds (those that are 10% fat or more) by multiplying the fat percentage (which is a number divided by 100) by pounds of feed per day. So, 1 pound of a 10% fat feed provides 1 x 0.10 = 0.10 pound of fat. If your mare has been getting about 1 pound of fat per 1000 pounds of horse per day she may just need a little pushing. If she has been getting less fat than this, try increasing the fat to see how she responds. If this is going to help you should know within a month or two. Good luck, and please let us know how things go!