We did a poll on our UK/Europe support group (2,600+ members) and owners reported around 30% of horses started on the initially recommended dose (usually 1 mg) had symptoms of the pergolide veil - off food and/or depression.
The FDA NADA for Prascend reported 33% decreased appetite and 10% lethargy as side effects of starting 1 mg (2 mcg/kg BW) Prascend - thelaminitissite.myfastforum.org :: FDA New Animal Drug Application for Prascend Sept 2011
The Equine Endocrinology Group recommends:
"Some horses show a transient reduction in appetite. It is therefore recommended that Prascend be introduced gradually by giving partial doses for the first four days or by administering half the dose morning and evening" - http://sites.tufts.edu/equineendogroup/files/2013/11/EEG-recommendations_-downloadable-final.pdf
France/UK Jan 2010