If you have injected a mob of cattle with a repeat-vaccinator gun, you will probably have experienced two common problems:
Both of these problems often have the same cause: incorrect orientation of the needle on the syringe.
A needle is a pipe cut at an angle with razor sharp leading edges. The objective when vaccinating is to get the opening of the needle resting between the skin and underlying tissues. This is achieved by orientating the needle so that at entry at about 45° to the skin, THE BEVEL IS PARALLEL WITH THE SKIN.
If the bevel faces away from the skin, the opening of the needle may still be in the dermis at first injection attempt, thus the high resistance. A more perpendicular entry is required to counter this, which results is the leading edge of the needle cutting into underlying tissues, with potential for intramuscular vaccine injection - thus the lumps.
I always have a pair of pliers in the vaccination kit so I can correctly orientate the needle. Easily done with a robust metal gun. But it can be a challenge with disposable guns.
Using the above approach, I rarely see vaccination lumps after using oil-based vaccines. And I rarely have injection problems - other than caused by faulty gear or cattle that think they don't want a needle!
Principal Scientist Agency for Food and Fibre Sciences
Department of Primary Industries
PO Box 976, Charters Towers, Qld 4820
Ph: +61 7 4754 6123 Fx: +61 7 4787 4998