I rescued a one - two year old female brussels last spring. She'd had a litter of pups and was pregnant when she was brought into the shelter -- later spayed. Her hair was fluffy all over at the time I got her. Over the summer the top layer of her hair on both sides has disappeared, leaving a smooth coat underneath. Should I be concerned?
Hair loss in a young bitch can be hormonal if the dog is not itching. Sometimes overproduction of the sex steroids can cause hair loss. Even though she is spayed, the sex hormones are secreted from the adrenal gland. Of course, over the summer months, the hair may naturally thin and regrow in the winter. There are seasonal hair loss patterns in some dogs. If the hair does not re-grow, then have her checked by your vet. If she is itchy, then have her checked sooner.