Boxer Aggression

Question
We two female neutered boxers ages 7 years and 14 months old who have lived together for 12 months without any problems.  They come and go through the pet door into our fenced yard.  They have played together and enjoyed being together for the past year.  Suddenly they have become aggressive.  We were giving them some treats outside and it was like a switch was thrown in their minds.  We are  not certain but it may have been the younger of the two who started who even so the older is unforgiving.  The older weights about 10 lbs less than the younger does which is 70 pounds.  We have always walked them on most days but since this incident we are taking them out twice a day for approximately 1.5 mile walks.  In the house we are keeping them separated and started showing ourselves as the pack leaders - We really need some advice / help on how to get over this situation.6V

Answer
Males are neutered-- females are spayed.

Seven years old versus fourteen months is a big difference and the oldest is the leader/alpha of the pack and the younger is challenging.

You cannot allow them to compete for treats or food-- and must set limits and boundaries of acceptable and unacceptable behavior.

The second one becomes aggressive and food aggressive, put her down to the ground/floor and hold until submissive to you. The alpha disciplines this way.

Try that for a few weeks.