Hi I bought my first pony in October he was 5 months old with handling has become very friendly. However he got infection and had to inject him with antibiotics . After the 3rd day he has become very aggressive and striking out at the front so much so that I couldn’t inject him. I asked a neighbour that has experience with horses and he couldn’t inject him either.He returns to normal manner again once not trying to inject him. Any advice would be appreciated. Elaine