Essential fatty acids (like omega 3 and omega 6 fatty acids) and fat soluble vitamins (Vitamin A, Vitamin E, Vitamin, D, Vitamin K). The plain fat is a nutrient too.
Kittens, generally, can begin to use a litter box at about four weeks of age, and a kitten being raised without its mother or adult cat will take slightly longer to litter train; so, keep this in mind when you begin the task of litter training your kitten. - Place the kitten in the box 1/2 hour after play or meals.
How to prepare for the birth: During the last week of pregnancy, the kittening box should be placed in a warm, quiet, draft free room which is off limit to children and other pets. She should be encouraged to sleep in this box. Obviously, food, water and a litter tray also need to be placed in this room.