I am a wildlife rehabilitator in Northeast Ohio. This was my 6th summer rehabbing. It is so good to know that there are vets out there that care for our little cottontail friends. Cottontails are my all time favorite animals and I love rehabbing them. They are a challenge, but that is part of the reason that I love them so much. I started rehabbing because I was an intern at a wildlife center that euthanizes all eyes closed bunnies that come in. The first time I was there and a tiny little tyke came in and I found out they were going to euthanize it; I just knew I had to help, so I took him home. He lived for14 days and then died, just as you described... doing well and then suddenly sick and dead within 24 hours. It was heartbreaking and I thought I wouldn't rehab anymore, but after the sadness passed, I found myself missing the feedings, missing the cuteness, and wanting desperately to have one live and be released. That became my mission. I wasn't successful that year, but the following year, I got a litter of 5 and 4 of them survived. I was ecstatic and determined to continue helping cottontails and to understand what was happening to the ones that didn't make it. No one at the wildlife center had a clue about bunnies and didn't really care. I would call desperate for advice as one was dying and they had nothing to offer. I tried researching online but just about everything said they didn't survive well in captivity and pretty much there wasn't any hope for the eyes closed guys that came in. I got lucky and found the answer I needed when one of my bunnies got diarrhea. I researched treatment for diarrhea and came across this website: http://www.squirrelworld.com/RabRehab.html. I was sad there was no hope for my little guy, but happy to have possibly found the info. I needed. Before reading that I didn't even know that bunnies did the cecotropes at night, I knew nothing about it. The following year I started adding the cecotropes (I already had a domestic rabbit) to their formula once a day for 3 days after their eyes opened and shortly after I got the litter of 5 where 4 survived. I used that technique for the rest of the year and had about a 33% success rate, which wasn't good, but not horrible considering I only took in eyes closed bunnies. My 3rd year of rehabbing, I decided to try using the probiotics instead of the cecotropes because my domestic bunny was getting older and not donating (that is what I call it :) ) all the time. Plus it was gross to mix it into the formula and I didn't have my own rehabbing space at the time and was heating it in the microwave and storing it in the fridge in the kitchen, so my mom wasn't too keen on that. I used LA 200 made by Fox Valley and it worked sort of. Some of the older eyes closed bunnies survived on it and even a couple 3-4 day olds, but my success rate dropped to 25% and they just seemed to be lacking something. So, I decided to go back to the other technique. I would take a big chunk of the cecotropes and mix it into a tiny bit of formula to make a very thick cecotrope/formula mix (I call it chocolate milk :) ) and gave each bunny 1 cc of the mixture. I did this once a day for 3 days starting the day the last bunny opened his eyes. After the three days, I would start them on clover, dandelion, plantain, oats, and timothy hay. This technique seemed to work well and my success rate went up gradually over the next two years to about 60% success. I was happy with this but still saw a lot of room for improvement. It was by chance that I came across what I think is the life savor for the tiny tiny little guys. I got in a tiny little gray guy as I call them in the fall of 2007. He was about 2-3 days old and had come into the center and left in a box overnight with no heat or anything. They sent his siblings home with another volunteer (they allow volunteers to take bunnies if they want to become super-permittees, but there were only a couple kids willing to and now they are all off in college and I am the only one that takes home the eyes closed cottontails :( ) and didn't realize he was in the box. The next day when the maintenance guy went to take the boxes, the little tyke started squealing and they found him and put him in with the others I was coming to pick up. So, I took him home with 5 other bunnies that were all 6-7 days old, just a couple days from opening their eyes. I had always thought that giving the babies the cecotropes too soon could cause gut issues, but the other guys were ready to get it and I didn't want to make them wait for nearly a week to get it in case there was a time frame after their eyes open that they needed it. I was at a loss with the tiny little gray guys at this point anyways (I had taken in over 10 over the years and none survived), so I decided to give the tiny little guy the cecotropes with the other guys and started doing alternate days cecotropes and LA 200 (because it takes forever to hand feed the "chocolate milk" to them). This worked well and all of the little guys survived. I over-wintered the tiny little guy and he made it until release the following May. He was big and happy and healthy. So, the mystery of the tiny tinies had been solved. Now that I give the cecotropes from day 1, my success rate has increased to about 75% living to be released. I am quite happy with that, but still don't feel I fully understand the cottontail. They are unusual little tykes and I don't know we will ever quite know what happens with them. I think stress and a sensitive stomach come together and are just too much for some. I find the way they interact to be quite interesting too. You will get some that are the best of buddies and are always together and if something happens to one, I have seen the other die of complete shock about a minute after his buddy goes. Then there are the ones that are loners. Fine with the others but not with any real buddies that they play with, just kinda hang out by themselves but peaceful. Then their are the ones with attitude that end up having to be separated because they beat the living daylights out of every other bunny, even siblings. Some are friendly to me; others will kick and bite me, freak out when they see me. You just never know what you will get. The other thing that I think effects bunnies in captivity is the stress. I have seen bunnies freak out and die, usually ones that come in older, but not always. You can just see it in their eyes. I used to hand feed my bunnies and they would struggle and not want to eat. I did my internship when I was in college and after taking in the first few bunnies and struggling to feed them all summer long, I realized there was no way I could continue rehabbing and go to school in the fall or rehab and work with how long it was taking me to feed each bunny. They got some little guys in one day and I refused to take them because I didn't have time. They didn't have anyone else to take them and asked if I knew how to tube feed. I didn't but the head of the center gave me a quick 5-minute lesson in tube feeding. That made my life so much easier and I have never had any issues with tubing bunnies. The only time they are difficult to tube is if they are dehydrated, then it is like their esophagus narrows or something and the tube won't go down. After they are rehydrated it is easy though, and I never have any issues. I now tube all my bunnies, it takes just 3 minutes to tube and pittle (stimulate them to pee) each bunny, which is so quick and easy and allows me to rehab about 100 bunnies a year. Something else I have done to reduce the stress is put green pillowcases over their aquariums when they open their eyes. This seems to calm them because they can explore their area, but don't see out to places where they can't explore (I think seeing places and realizing they are trapped and can't go where they want to stresses them out) and they don't see me walking around and feeding everyone else. When they are older and move to a bigger cage, I use a light blue sheet and put that over their cage. The green is for the grass which is about all the little eyes just opened bunnies would see in the wild and then the light blue is like the sky which is what the older guys would see. This seems to calm them and has worked quite well for me. As for amounts that I feed and formula... I feed 10% of their body weight (only up to 6 ccs though, anyone over 60 grams just gets 6 ccs because they are usually about ready to start on greens and I don't want to overfill them if they have eaten some greens) 3 times a day. They go down to 2 times a day formula feedings when they are 70 grams, then 1 time a day when they are 80 grams, and I wean at 90 grams. This has worked well for me. I have found the Zoologic 33/40 mixed with Multi-milk works the best. I have tried Fox valley formula but didn't like it and they seemed weak with possible bone deformities on Esbilac and Multi-milk and several died, so I switched back to the Zoologic. There have been issues this past year with Petag products though, and I am not too sure what I will do in the spring. I was hoping everything would be resolved by now, but it doesn't look like they are going to change anything back. Sorry this is so long, I LOVE cottontails and could talk about them for hours. I would love to hear some of your techniques with bunnies and what formulas you have had success with.