If you own a pair of unfixed, sexually mature female dogs, they'll both regularly go into heat, no matter how much you dread it. This usually happens about two times a year. When female dogs share living environments, they frequently go into heat at the exact same times, although not in all cases.
Aggression in Heat
Separating female dogs when one is in heat or both of them are isn't always necessary. As members of the same sex, they're incapable of breeding together, which throws the concern of pregnancy out the window. Separation sometimes is necessary, however. Increased aggression is a typical sign of heat in canines. Unspayed female dogs are often particularly truculent toward those of the same gender, indicates authors Terry Albert and Debra Eldredge. If you're worried that your hormonal in-season pooch might behave violently toward your other female dog, separate them immediately. Worse yet is when they're both hormonal and feeling aggressive. If you don't separate them, you could risk one -- or both -- of your precious pets getting seriously hurt in a scuffle.
Aggression isn't the only undesirable behavior common in dogs in heat. When female dogs are in heat, they tend to exhibit unusually cantankerous behavior. They whine a lot, often for hours at a time. They're fidgety. They're anxious and stressed out. They frequently try to break free of their homes to look for breeding partners. If you feel that the presence of the other is making the pooch in heat feel even more distressed, then you might want to split the two up temporarily. By doing this, your home might become a bit more peaceful and quiet for the remainder of heat.
Separation From Males
If your unfixed female dog shares a home with an intact male dog, you definitely want to separate them while she's in heat, otherwise the chances of her getting pregnant are practically inevitable. If you have two intact male dogs, you also want to keep them away from each other when an "in heat" female is in the residence. Otherwise, it could lead to intense -- and extremely dangerous -- aggression between them. Male dogs get highly competitive when it comes to mating access.
Having dogs in heat can be a headache to all involved, including the poor frustrated pooches. Thankfully, you can do something about it. If you spay your female dogs, they won't go into heat anymore. They, as a result, also won't experience any of the effects of the cycle. Importantly, they won't be able to get pregnant. Although male dogs don't go into heat, neutering them can stop them from exhibiting hormonal behaviors as well, whether they pertain to aggression or territorial actions such as urine marking or whining. Discuss fixing your dogs with a veterinarian.