HELP!! Chicken Attacked Under-belly ripped open, what can I do?

I have seen chickens heal from wounds that bad.  Keep putting the neosporin on daily and if you see any signs of infection like pus or a bad smell develop, then get some Penicillin G injectable at a feed store and dose by her weight.  You might want to clip away some of her feathers around the wound.

keep it clean and keep her indoors if you can.  Put neosporin on it daily.

i had a turkey attacked by a fisure cat i shot the fisure cat before it could kill her if you keep the woond clean and dresd and hep her inside she should be ok give her penicillin and clean the woond with iadine or betadine you can stop bleeding with corn starch or you can get septic powder and it is great i use it on all my birds woonds you can steralize a wood burning tool and quaterize woonds if really needed  keep neosporin on it also go to cvs and get some cream called silver gurd or any mrsa protester a staff infection can be fatal on a deep woond any precaution you take aganstit will help i belive 70 or 91 precent alchol is best it is what i use it hurts them for a second but will save them in long run e mail me if i can help more ..dannypaquin76@yahoo.com

The last bird that we had that was attacked by a dog(s) was missing the feather and top layers of skin in a 5" by 7" area, had a puncture wound in the muscle and survived. Clipped of the loose skin and removed feathers around the wound. Used peroxide to cleanse the wound, then rinsed with soapy water, then rinsed with diluted betadine, on the wound we put antibiotic cream on a gauze 4x4, saran wrap on top of the gauze ( used antibiotic cream in between the gauze and saran wrap to hold them togather)  wrapped her wound loosely with vet wrap, Don't cover her vent or put her crop in a bind with the vet tape, gave her about 3 injections of antibiotics over a 10 day period, had to cleanse the wound and redress it daily. Penned her up with food and water so the others wound not pick at the dressing. Had to wet the 4x4 gauze with warm water to remove it, did not want to pull it off and make the area bleed.  She was not very cooperative during the whole process, this happened last fall, this year the turkey hen has been breeding and laying eggs, brooding, all of the feathers did not regrow, she has a bald area on her breast/side area, she lost a lot of weight while she was healing up. I was surprised that she survived. i lost about 5 chickens during a 2 week period due to roaming dogs. No more losses after we put up electric strand around the top and bottom of our 5 foot fence. lots of unhappy dogs though, you could hear them yelp from inside of the  house when they got hold of the electric fencing.

BUMP! Poor Baby!!  This is my first flock too. I can only answer on the feathers - I think trimming them down is just fine (plucking them might irritate it more?) My leghorn injured her foot and I had her in a chicken hammock for awhile, trimmed off all the feathers around the vent and it's been 6 months, she still has a bare bottom lol 

I can tell you from my experience so far... One of mine was attacked by a weasel and right now I'm giving her Duramycin-10 - the dosage for her is 3/4 tsp per quart or 1 Tbsp per gallon (confirmed by a pharmacist), searched through many threads to get this info, and flavored the water with strawberry jello mix. I was also told to give it to her for 20 days vice 10 days. I hope someone can tell you the exact dose.  I have talked with quite a few people about cleaning the wounds, most of them vet techs who recommended just a saline solution for cleaning: 1/4 tsp non iodized sea salt per 8 oz warm water - especially if you think the soapy water is irritating it more.  They all said DO NOT use peroxide.  (I have 2 avian vet clinics in town and both avian doctors were out of town).  

ETA: someone told me about Wonder Dust - I was also told to avoid putting any creams or ointment on it so it can "dry out" - another one told me about raw honey, but worried about the flies (I'm in NC, the flies are bad right now). Again, this is just from my experience, so it won't work in every case. Here is the thread on mine to watch how her wounds heal.

http://www.backyardchickens.com/t/664284/possible-weasel-attack-old-wounds-on-neck-gaping-holes-updates-pic-heavy-graphic

I also wanted to mention, when my chicken injured her foot, she didn't eat very much and was in a lot of pain, I cut up baby aspirin and gave her 1/4th of the pill (crushed up in vitamin water flavored with jello mix 2x per day).  Also, she had no desire to eat but whenever I put scrambled eggs or chicken flavored ramen in front of her she ate it up. I also put frozen veggies in the ramen so she could get some vitamins. Her poop was a little runny during these times, but once she started eating her regular feed, her poop was back to normal. I didn't think she was getting better (after almost a week) I started looking up humane ways to put her down, but kept on persisting and now she's back to her regular self (more people friendly too!) 

ETA: soggy dog food, or soggy chicken feed might entice her to eat a little more. She'll also stay hydrated (very important)