After winter fur coming off and brushing more, I noticed a major swelling in the scrotum area. It is a 18 yr old who was with a pregnant mare till appr 2/3 mo's ago. It appears to be the testicle rather than a growth , but not sure. It is very firm and about the size of a softball. He is not in pain, gets very excited when a mare stalled next door, and had dropped when a mare in heat was close. Could it be from a kick perhaps or? The vet will be attending , but somebody on this form has usually encountered something similar. Would appreciate views.