There has got to be an easier way. So you have to hold each bird and weigh it, 60 times? That’s just not plausible.
If it were me with sixty birds I would group them as suggested by
@dawg53.
Example: weigh say 3 birds in a group and avg that weight.
Then dose them. You might be surprised of the weight variation. Which could be a good thing. That way you will know more about those that might be too under weight.
Having & raising 60 chickens tells me you have a good system going so, don't chance losing your birds to some parasite that you have control over to kill. Losing birds to something out of your control is one thing, but our girls and boys need our help sometimes.
Gather your siblings, friends ect. And a have a chicken deworming party!
Make it fun, not a laborious task.
After all, your the keeper of 60 chickens and we are the ones giving you advice to care for them.
As you know, chickens take care and in return, they produce eggs for us without any complaints and put lots of smiles and conversations on our faces.
So, when it comes time to deworm, make special feed for the sick ones or fix a bumble or suture a wound, its what we do in return.
So, make a plan, gather people to help and "Just Do It!".
Like Dawg53 said, it took him 20 min to do 21 birds.
Do it at night roosting time.
Then you can get/catch each one.
If I lived closer, I would help you.
Keep us posted.
Your chickens will thank you and produce many safe eating eggs again.
I couldn't image having worms coming out of my butt.
Now...THATS GROSS! Lol