Is there any side affects when my horses get sleeping sickness shots?

PLEASE answer I just gave my horses sleeping sickness shots yesterday morning and my gelding ate all his feed but one of my mares bareley ate any feed and was laying down in her stall the other mare didn't eat much of anything either but she was standing. When I let them out they would not eat any grass but they would just stand there the mares layed down but I made them get up last time I went out they were none laying down but they all would just stand there could someone have poisoned them? Or are these some side effects from the sleeping sickness shots?