What Would Cause Hair Loss in Healthy Little Dogs ?

We have 2 female Miniature Pincher's about 3 years old. They both have a hair loss , and it is in a pattern on them, it has been progressive so that now only the backs of both dogs have a normal amount of hair. With one of them, it began when she had a cyst operated on and removed at the base of her neck, on... show more We have 2 female Miniature Pincher's about 3 years old. They both have a hair loss , and it is in a pattern on them, it has been progressive so that now only the backs of both dogs have a normal amount of hair. With one of them, it began when she had a cyst operated on and removed at the base of her neck, on top, where shots are normally given. The vet surgeon told us that at that time, perhaps some bacteria entered with the needle and that was the probable cause. Whatever. Then her sister started the same thing. Our vet advised that it may be a hormonal problem, not uncommon in little dogs, they are both under 5 pounds, and he gave us medicated shampoo and advised use of benadryl. The hair loss continued but slowed, maybe.

Now I have been reading about hair loss and for humans, we need protein, iron, most of all, increased in our diet. I have been giving vitamin supplements to them that I got from the vet but so far, no obvious regrowth. Oh, yes, also omega fish oil, that was recommended to give them *and for us to take also*.
Another interesting thing to me. We have another min pin who mostly plays outside and he has experienced NO hair loss. I am wondering about all this.

I have learned so much from others on Yahoo Answers in the past, I hope someone may point me in the right direction again. In the past for example, I had never heard of Capstar until one kind girl on YA told me and I shall forever be grateful to her. Capstar solved our problems. We have 9 dogs and as many cats. Thanks all.
Update: Kathleen, I did suspect allergies and we put the dogs on California Natural varieties, no artificial anything and a bit expensive. The love it but still aren't growing the hair back. It's been a while. Baths are not more than once a week, or two, they are indoors most of the time so aren't dirty. We... show more Kathleen, I did suspect allergies and we put the dogs on California Natural varieties, no artificial anything and a bit expensive. The love it but still aren't growing the hair back. It's been a while. Baths are not more than once a week, or two, they are indoors most of the time so aren't dirty. We use the medicated shampoo from the vet and also the AllNatural Oatmeal Organic. We take more care for our little dogs than we do for ourselves !
Update 2: Jake ! You may have hit the target. I have been gone a lot, doing surgery in Central America, then 3 more weeks doing dental work, and a month with my grown kids away also. I wonder if it could be. The dogs definitely are ''my'' dogs, and prefer me to any family members when I am home. ... show more Jake ! You may have hit the target. I have been gone a lot, doing surgery in Central America, then 3 more weeks doing dental work, and a month with my grown kids away also. I wonder if it could be. The dogs definitely are ''my'' dogs, and prefer me to any family members when I am home. Although they seem to love everybody, almost, it's clear that they consider me The Place to Be. You have opened up a new area of consideration for us Thanks.
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