I read your post in the newbie section, and if i remember correctly, you said you were new at the cattle thing so...
Cows/calves get the shot in the neck and not the rump because the poor cuts of meat are in the neck and the sweet cut of meats are in the rump.
Injections cause damage to the meat, meat gets chucked at the butcher table.
Guideline is no more than 10cc in the one site, so you got to re poke if there is more than 10 cc.
IM is Intermuscular
SQ is under the skin.
Not all drugs are rated for both. There is one antibiotic that is given in the ear, gentlely i might add.
Do not mix drugs..a given
There are different size needles for different jobs
cows need 1.5" or greater, cause they have a real thick hide (close to 1"), would not believe it if i hadn't seen it myself in an older cow in the winter.
Calves are smaller
different guage
TALK TO A VET about the where why and how about injections! Please. Not to be rude, but what is done in the rump and the neck effects all of us. Injection lessions are a problem for packers, they end up tossing meat or down grading it, cost them money, slowly filters down to the feed lot and then the producer.
customers do not like it much finding a damaged chunk in there best Sunday roas either!
JMO
RR