one of my baby guinea pigs isnt growing?

Question
My sow has given birth to 7 babies in the past 4 weeks. Sadly 4 were still born, and one died 24hrs later.  But we are blessed with 2 georgeous babies which we are unable to tell the sex of, they are still living at home with their Mom.  They have stopped suckling from her, and eat from the bowl.  One particular baby I am growing increasingly concerned of, is not putting on any weight or getting any bigger.  The other sibling has doubled in sized, yet the small baby still looks only a few days old.  The baby is very lively and is constantly standing in the food dish and tucking in.
I took the Mom and babies to the vets a few days ago, because Mom has a skin infestation, causing her to go bald and she is scratching badly.  The vets gave me Xeno 450 spot-on, which I haste to say is a strong chemical and cannot be given whilst Mom and babies are still together.  The babies are also scratching,(no bald patches) but cannot be treated as they are under the 450grams for a spot-on treatment.  The larger baby got weighed and was approx. 200grams, therefore both are untreatable.  The smallest baby has rough skin on its tummy, I can only compare this to looking like a plucked chicken skin? My concern is, I don't want to use the xeno spot-on and after looking up an alternative on the internet, I am now waiting for a delivery of Neem oil to bathe them all in, and hopefully that will work,I know it will be safer.   Otherwise, what can you tell me about the underweight baby?
look forward to hearing from you very soon, regards Mandy

Answer
Hello Mandyjane,

I'm assuming the infestation is mites? If so, this could be the source of the baby's problem. Until you are able to treat him, force feed him. If you can get critical care from your vet or directly from the Oxbow website:

http://www.oxbowhay.com/link.sp?page=CriticalCare

That's the best. If not, crush his pellets and mix them with water and feed him with a syringe. Baby Oatmeal Cereal will help get his weight up and I recommend using that for at least one of his feedings. Feed him about 3 - 4 times a day (actually, I recommend one oatmeal feeding a day for the larger baby too to help get his weight up so he can be treated sooner as well). Your baby may just be a slow grower, it happens sometimes, especially if he was the runt, and supplemental feedings are usually helpful, however, the fact that he is suffering from parasites is a concern. Make sure he eats and drinks. If there are any other signs of trouble (lethargy, discharge from eyes or nose, etc) see the vet right away. Hopefully he'll start putting on weight and growing soon. Good luck. You and your babies will be in my thoughts.

-kkat
www.geocities.com/abyssinianguineapigs