horse behavior around mare

Question
i have just bought a 8year old gelding around 2 months ago. the problem i have just started a couple days ago. there are three other horse in the field 2 geldings and 1 mare. my horse all of a sudden has been acting totally different. the person who owns the other horse have had him lung and try to bite him. he tried to do the same thing to me to. he told me that it was the sweetfeed he has been feed. but i was thinking she is in heat. is there any sign of know this is the case. and what should be done to keep this matter from getting worse.   thanks

Answer
The first thing I would see is if when the gelded your horse they removed both of the testicles and cords. He could have a testicle that  did not drop and he is has testosterone. If that is the problem then you can have him "regelded". I would also cut out the sweet feed and feed him pellets and beet pulp. Make sure he has either pasture or free choice hay. Most horses do not need grain unless they are working alot.

Lisa