Yes you're right in what you say Womble. However some years ago you could get Panacur worming buckets which you gave the relevant animals access to for about a month. I only ever used one once (on my sheep) as the buckets went out of favour, but it did cure a worm resistance that I had at the time. From that I concluded that hitting the worms for an extended length of time was actually more effective than a once off dose. Not very scientific, I accept, but I didn't have the facilities for a full scale double blind, peer related trial. The system worked for me, so I was happy.
In addition, the safe margin for Panacur is very high. (You can look it up.) So, having read that for small animals, (and for equines) Panacur should be given over several days, I often administer it to my animals in this way also.
(This isn't an opening for another lecture on faecal egg counts and worm resistance etc
. Just bear in mind folks that this is a forum and the question asked was "How
do you give wormer?" I have merely answered the question. )