improved daily ration mammal feeds are provided which include minor amounts of heartworm preventative drugs , ensure that a mammal consuming the feed receives quantities of drug sufficient to establish and maintain substantially constant concentrations of the drug in the pet &# 39 ; s bloodstream . the feeds may be produced by extrusion with addition of minor quantities of heartworm preventative drug so as to uniformly distribute the drug throughout the extruded product . ivermectin levels of from about 2 - 1500 μg / kg of extruded feed are preferred .