My dog had her first menstruation. On her 2nd day of menstruation, she loss her appetite. She doesn't want to eat anything. We're afraid of what's happening to her. Is it normal for a dog to lose appetite during this period? I already send her to the doctor. She has given dextrose for 24 hours. We are very much affected by this because we love her so much.

This could be minor, or it could be major.

Since this is her first cycle, she could be experiencing abdominal cramps. Just like when we have our period, we can have cramps strong enough to nauseate us. That could be her problem.

The other issue that I think of, would be going on inside her. Pyometra typically doesn't show up until after their cycle is complete, but it could be something similar.

Your best option to avoid issues such as these, is to get your dog fixed as soon as possible. Speak with your vet and ask if it is OK to get her spayed during her cycle.

Contact your vet.