Things may have changed but back in the day ranchers could buy and administer their own medicine. What they bought for livestock was the same as used in humans in many cases. The human dosages were printed on the labels.
One tough old bird had a nagging cough and decided a penicillin shot as in order. Why see a doctor when his brother in law had penicillin, syringes, and needles? Save a few bucks, no?
Down at the barn he dropped his pants and bent over. The forthcoming bellow would have shamed a bull. Evidently the size of needle and the technique for humans is different than cows. Who knew?