Actually I should say this....they can and probably always have some worms but a very low count is ok maybe. When it is high and you see them in their poop, the animal needs to be treated for worms.
The only way to maintain the worms in the animals system is to do a fecal test every so often like every 2-4 months and then treat if needed or just treat for worms routinely on schedule.
I just sent a fecal sample off to WSU to see if my goats had worms and the result was not even one egg or worm...so they got no wormer and even the cocci was very very low so no treatment need on that either. I only did the test this one time since I just inquired these goats on May 1st and I treated them x2 with 2 different types of wormers. My point in doing this was not that I seen worms but to eliminate the reason of their big stomachs to being worms....and I wanted to make sure what I treated them for worms actually worked.
So they are either pregnant or just fat. I gave up and think it is the later nowadays....tired of waiting lol.
I don't send of fecal test usually however; horse, chickens, pigs, goats will get routine worming here at our place.
Whenever I get a new animal unless proved to me otherwise, I give everything like they have never had it before. These goats came in bad condition so it was very obvious they were not cared for properly, prior to coming here.
Hope that makes sense and sorry for getting a bit off topic!