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.
Learn how to determine kitten age. *Note: Alley Cat Allies does not recommend attempting to socialize adult feral cats or kittens older than four months of age. Kittens who are at least 8 weeks or who weigh two pounds can be simply trapped, neutered, and returned to their colony. Learn more.