I would just like to make a point about "negative" fecal results. Fecal samples are checked for worm eggs, not adult worms. Intestinal worms shed their eggs in cycles, usually about 10 to 14 days. It IS possible for an animal to have worms, and have no eggs appear in a fecal sample, if the worms are in a non shedding cycle.That is why lab reports usually say "no parasites found" rather than negative. Ideally, you should run 2 tests, about 2 weeks apart.
Case in point, back when I was working for a vet, I picked up a stray cat, (which I ended up keeping) and I checked her stool the day after I picked her up, and found nothing at all on the slide. I checked another sample in 2 weeks, and the slide was wall to wall roundworm eggs. In 15 years working at that vet hospital, I never saw an animal more loaded with roundworms.
This is why it is recommended to worm twice, 2 weeks apart. Wormers kill adult worms only, and there may be eggs in the intestines that will hatch. If you worm again in 2 weeks, then you get the newly hatched worms, before they also lay eggs.
Case in point, back when I was working for a vet, I picked up a stray cat, (which I ended up keeping) and I checked her stool the day after I picked her up, and found nothing at all on the slide. I checked another sample in 2 weeks, and the slide was wall to wall roundworm eggs. In 15 years working at that vet hospital, I never saw an animal more loaded with roundworms.
This is why it is recommended to worm twice, 2 weeks apart. Wormers kill adult worms only, and there may be eggs in the intestines that will hatch. If you worm again in 2 weeks, then you get the newly hatched worms, before they also lay eggs.