See this article: http://jat.oxfordjournals.org/content/32/8/667.full.pdf
I assume you have googled both of these chemicals. I too have horses but am not involved in the racing scene. I don't know any supplements off the top of my head that would result in your findings but am guessing it is not from a packaged feedstuff! Start by finding out exactly what was fed and what meds were administered to your horse in the last few days before the drug test. It may be best to direct your inquiries to your veterinarian or a veterinary discussion site
I believe that both these might be used for cold or allergies in man or horse. From the info below, I would assume that these both can have performance-enhancing effects in racehorses.
pseudoephedrine (aka Sudafed)) see Pseudoephedrine - Wikipedia, the free encyclopedia
"O-Desmethyl Pyrilamine is a metabolite of the antihistamine Pyrilamine."(http://www.scbt.com/datasheet-391550-casnumber-57830-29-2.html);
for info on Pyrilamine, see Mepyramine - Wikipedia, the free encyclopedia