With our fixed population of all adult horses, just our own horses,
this has worked great. We have always gotten a lot of comments of how
good the older horses looked for their age, never had to dump feed into
any of the horses to keep weight on etc. I seem to remember seeing an
article in Western Horseman years ago about how frequently worming with
ivermection was resulting in older horses no longer building resistance
to worms like they used to (older products didn't get such a complete
kill or something like that.) The article mentioned that some research
was being done in the direction of trying to generate a "vaccine" that
could be given to generate the resistance that horses used to build up
over time. I imagine the economics were such that not too much money
was invested in this research - Why come up with a one time "vaccination"
when you can sell people wormer 8 times a year for the life of a horse?
I know I've never heard any more about the concept.
Anyhow, with the new information I've heard about the possible risks
with on the dot worming and the good history we've had with our lax
worming schedule I don't intend to change my ways in the near future.
Teresa and Grey Moun (off to the MRER benefit ride this weekend yeah!)