The 8-way vaccines with clostridium aren't a problem, and the respiratory vaccines didn't used to be a problem. This time, it got all over my hands when the bottle leaked, and it is oily. I use a 16 needle, and if the needle is sharp, that is, used on fewer than 8 animals, it penetrates fine. It is the plunger in the syringe that is the problem. For the first few doses it is fine. But after that, it is as though the vaccine deteriorates the rubber in the syringe or something. I finally finished the vaccinating successfully the second day by changing the 35 cc syringes every time I emptied one. (One syringe delivers 7 doses at 5cc/dose.) So now I am curious. If the vaccine is deteriorating the rubber or plastic in the syringe, it doesn't seem like a good thing to have it going in to your cattle.
Also, we all tried it. We used SQ techniques, (pulling up on the hide when injecting) as well as rapid techniques (coming in from the top in a squeeze chute that is not well designed for vaccinating) Once the syringe started resisting, none of us could get it to work easily. Those with the strongest hands ended up giving the vaccinations.