Yesterday my vet came out to check on my mare, because she cut up her legs. After the vet looked at the cuts he gave her a shot of antibiotic. He gave half the shot in her neck, and half in the left side of her chest. The needle was pretty large, and he stabbed it in her pretty hard. This afternoon I was with my horse and I noticed the left side of her chest where she got the shot was really swollen, and where the needle had gone in was like a hard lump. I rinsed it with cold water but I can't tell if the swelling went down. She has been eating and drinking fine but seems pretty lathargic.