Hi, a good rule of thumb to start with is to feed between 2 - 3% of your dog's bodyweight (if adult) per day, therefore if your dog weighs 24kg you would be feeding between 480-720 g of food per day.
(the formula is 24/100 x 2 or 3) :D
However this is just a guide some dogs do well on considerably less and others need more depending on sex, time of year, activity levels etc etc etc.
Colitis is an inflammatory condition which develops when any animal eats something that does not agree with it.
It is not a disease in itself.
The way to avoid it is to feed a species appropriate diet.
I feed raw from 7 weeks of age; most medium to large breeds are perfectly well equipped in the dental department for managing whole chicken wings from this age; mine also get carcases at this age and when they get to about 12 weeks thighs, drumsticks and quarters are introduced along with all sorts of other sources ie pork, lamb, beef, venison, turkey, duck and whatever I can get my hands on which is cheap.
I have been feeding this way for nearly 4 years and none of my dogs has ever had a problem with any bones. (What does your husband think they eat in the wild?)
They get some fruit and veg each day, whatever happens to be cheap and available. Bananas and avocados for example they can eat as is. The rest takes a couple of seconds in a blender.
They get fed kidneys, lungs and liver regularly with some live yoghurt (the only dairy I allow), raw eggs and raw or tinned fish.
I feed no grains whatsoever, again in the wild they would not consume cooked processed grains; there is no proven need for carbohydrates in a dog, even the pedigree website admits this! ;)
I add Keepers Mix, Vitamin C, Vitamin E and Fish Body Oils to the diet and that is basically it.
For more news on diets and specifically colitis etc please look at
http://www.dogaware.com