I work with an animal rescue agency in Mississippi. We have over 50 TNR colonies that I am aware of. There are 3 ways to TIP the ears:
1. Hole punch (middle area of the ear just like a paper hole punch).
2. Ear tip (there is modest and extreme versions of this) It depends on the vet & your request.
3. Ear notch (“V” shaped removal of tissue).
I prefer a moderate amount of the TIP to be taken off (adult cat around 0.5 to 0.75 of an inch). The V shape looks too much like a fight mark. I have never seen the PUNCH method but it seems that it might be hard to visualize without back lighting. Why moderate ear tip? Reason being I have recaught and knocked out an many cats because the ear tip was SO subtle that I could not tell it had been done.
I will remind you that TIPS are done on cats that are NOT friendly. Strays that are sweet and nice- I would never do that. But when you are talking 50 + cats and one brown tabby looks like another.
In terms of vets re-opening an abdomen: new closure methods can be so good that you cannot see a scar. And the reason boys also have tatoos on their tummies: if they are neutered when they are young, they look like a girl! Also there are some techniques to do a SIDE spay. They go in on the side of the cat. Very safe but no scar to be felt!
HSUS suggests that 10 oz is the smallest size a cat must be to be spayed or neutered if the testicles have dropped. Too many adoptors end up with accidental births so anything I adopt out (around 1000 a year) is already spayed or neuterd. Our new low-cost spay & neuter clinic will do at 3 lbs if it is has a human or just under 2 lbs if it has yet to be adopted. The smallest I have done is 20 oz but I generally do not adopt 10 oz kittens…too tiny for most homes.
There is substantial evidence (JAVMA vol 233 no 1 July 2008) too many old school vets are wanting to wait until they are 4–9 months old, but if a cat can begin reproduce starting at 4 months….WHY WAIT!
I look forward to a day when there are no more homeless animals. But right now my state (MS) euthanizes 73,000 homeless pets per year. Everyone in every state puts down too many…more than zero is too many!