My name is Jane. I have been working professionally with animals especially dogs in both health and behavioral issues for over 18 years. I have over 14,000 satisfied customers. It will be my pleasure to work with you today.
While there are medical causes for sudden aggression, it does sound more like a dominance issue than medical. However I want you to have the information just in case. You can read about this here.
When a dog is a puppy (under a year of age or so) any older dog in the house is the alpha dog. A male is usually alpha over females and females have one female alpha in addition to an alpha male. In addition, when a new older dog is added to a household with an older dog, usually the older dog is seen as the alpha initially. In many cases, two dogs will be perfectly fine with the status quo until you add a third dog. That can trigger the first two to start fighting as the younger of the two dogs feel they might be a better choice as the boss or alpha. Sometimes it is because the younger dog is stronger, or healthier or that the older dog has an undiagnosed condition.
Sometimes it will look like one dog started a fight, but with dogs a wrong look or movement by a lower ranking dog can trigger a fight. For instance, if a younger, lower ranking dog starts to eat first or pushes past the alpha, that can be a sign of disrespect and the older dog would need to reprimand the lower ranking member or lose their position as the leader.
You may also be confusing the issue for the dogs. In a pack, the leader or boss of the dogs should be fed first, get affection first and be the first one out the door. If you show another dog attention before the alpha, it can make the lower ranking dog feel that you feel they are a better choice. So you need to pick the boss and show that dog attention first until they, feed and give treats to that dog first. You also need to establish complete control over that dog as well. If the younger dogs see the alpha obeying you, they will obey as well.
I would start practicing their obedience commands with them. The following site is helpful for teaching you how to train your dog. Be sure and click on the link to the page on obedience at the bottom. and links on subsequent pages leading to detailed instructions.
I'd try and do at least one 15 minute session for each dog every day. I would start making your dogs work via the Nothing in life is free program (NILF). It is outlined below. These things will establish you as the ultimate boss.
You will also want to keep a leash on the females at all times initially to grab if they should disobey. Dogs like knowing what is expected of them and they love the little paper thin slices of hotdogs (vienna sausage) or liver slivers that I use for treats while training.
Additional training can also help. Both dogs should be leashed and if one dog even looks at the other dog, a correction should be done. Any sign of aggression including a prolonged look, hair raised on the shoulders, a growl or even a stiff legged walk, should be corrected. A correction is a quick tug of the leash and a firm low toned "NO". Once you have done this couple of times, you should notice the dogs ignoring each other. When that happens, you will want to reward them for the desired behavior. Again, use tasty treats like the hot dog slices. This teaches the dogs that you WILL not tolerate fighting in YOUR pack.
I also want you to study the sites on body language. These will help you determine if the dogs are being dominant, aggression or playful.
I know you have a trainer coming and that is helpful as well, but you need to work with your dog regularly to achieve total control over the dogs and stop any fighting between them. Living in a household with multiple females can be an issue. Some owners end up just keeping the two separate to avoid these problems. You can read about this issue here:
In addition, if the situation is not improving using the techniques I describe, you may have to consult a professional behaviorist. You can usually find a behaviorist by asking your Vet for a recommendation or you may be able to find one using the following site.
I hope this information is helpful to you and you are satisfied with my response. If you would like any additional information or have more questions please don’t hesitate to press the reply to expert or continue conversation button so I can address any issues you still have .