How often do you dose the horse with penicillin?

You can give it to a horse via intramuscular or subcutaneous. With IM you will want to completely sink the needle into the horse and pull the plunger slightly to ensure that there is no blood (because you don't want the penecillin going into the veins, only muscle) and if there is no blood push the plunger to inject the penecillin. If there is blood you need to pull out and start over.

As for where, it has to be in a large muscle area such as the side of the neck or the rump. You also need to put it in a different area each time. The penecillin makes them sore and causes a lump at the injection site.

How much depends on the weight of the horse. 1 ml for each 100 pounds of body weight. You can find this out by weight taping them. Also, you would give more if they seem to need it because of infection. However, you would not give it to them if they have no infection.

Ensure that you are using clean, new needles each time. You can cause a secondary infection if you inject them with a dirty needle.

And finally, you would give it to them for at least one week but no more than two. If you do not continue with giving it to them the same time each day you would be doing this for nothing. For major infections you would dose 2 times a day for one or two days and then once per day. However, it is much more highly recommended to follow the instructions on dosage and length of treatment for your horse as mentioned on the bottle, on the carton that comes with the bottle, the pamphlet that is in the carton with the bottle, or what is recommended by your veterinarian. Avoid terminating treatments when the horse looks like he is getting better and you still have several injections to go, because chances are a relapse may occur making the illness or infection worse than before.