public class Animal
    {
        public string Name { get; set; }
        public bool IsFed { get; set; }
        public List<FoodName> ConsumableFoodList;
    }

    public class Cat : Animal
    {
        public Cat()
        {
            this.IsFed = false;
            ConsumableFoodList=new List<FoodName> { FoodName.Milk, FoodName.Meat };
        }
    }

    public class Dog : Animal
    {
        public Dog()
        {
            this.IsFed = false;
            this.ConsumableFoodList = new List<FoodName> { FoodName.Crackers, FoodName.Meat };
        }
    }

    public class Mouse : Animal
    {
        public Mouse()
        {
            this.IsFed = false;
            ConsumableFoodList = new List<FoodName> { FoodName.Crackers, FoodName.Cheese };
        }
    }

    public enum FoodName
    {
        Crackers,
        Cheese,
        Meat,
        Milk
    }

static void Main(string[] args)
        {
            List <Animal> myAnimals = new List<Animal>();
            myAnimals.Add(new Cat());
            myAnimals.Add(new Cat());
            myAnimals.Add(new Cat());
            myAnimals.Add(new Dog());
            myAnimals.Add(new Dog());
            myAnimals.Add(new Mouse());
            myAnimals.Add(new Mouse());
            myAnimals.Add(new Mouse());
            myAnimals.Add(new Mouse());
            myAnimals.Add(new Mouse());

            foreach (Animal myAnimal in myAnimals)
            {
                Console.WriteLine(myAnimal);
            }
        }

        List<FoodName> randomizedFoodsStandard = RandomizedFoodsStandard<FoodName>(); // работает

        ...

        public static List<TClass> RandomizedFoodsStandard<TClass>(int amountOfFood = 40)
        {
            List<TClass> randomizedFoods = new List<TClass>();
            var rand = new Random();
            int enumerationSize = Enum.GetNames(typeof(TClass)).Length;
            for (int i = 0; i < amountOfFood; i++)
            {
                randomizedFoods.Add((TClass)Enum.Parse(typeof(TClass), rand.Next(enumerationSize).ToString()));
            }
            return randomizedFoods;
        }

        List<FoodName> randomizedFoodsLambda = RandomizedFoodsLambda<FoodName>();

        ...

        public static List<TClass> RandomizedFoodsLambda<TClass>(int amountOfFood = 40)
        {
            var rand = new Random(DateTime.Now.Millisecond);
            var randomizedFoods = new List<TClass>((IEnumerable<TClass>)Enumerable.
                    Range(0, amountOfFood).Select(i => (FoodName)(rand).Next(0, 4)));
            return randomizedFoods;
        }

        List<FoodName> randomizedFoodsLambda = RandomizedFoodsLambda<FoodName>();

        ...

        public static List<TClass> RandomizedFoodsLambda<TClass>(int amountOfFood = 40)
        {
            var rand = new Random(DateTime.Now.Millisecond);
            var randomizedFoods = new List<TClass>((IEnumerable<TClass>)Enumerable.
                    Range(0, amountOfFood).Select(i => (FoodName)(rand).Next(0, 4)));  // не могу убрать FoodName
            return randomizedFoods;
        }

        List<FoodName> randomizedFoodsStandard = RandomizedFoodsStandard<FoodName>(); // работает 

        ...

        public static List<TClass> RandomizedFoodsStandard<TClass>(int amountOfFood = 40) // Всё обобщено
        {
            List<TClass> randomizedFoods = new List<TClass>();
            var rand = new Random();
            int enumerationSize = Enum.GetNames(typeof(TClass)).Length;
            for (int i = 0; i < amountOfFood; i++)
            {
                randomizedFoods.Add((TClass)Enum.Parse(typeof(TClass), rand.Next(enumerationSize).ToString()));
            }
            return randomizedFoods;
        }


        List<FoodName> randomizedFoodsLambda = RandomizedFoodsLambda<FoodName>(); // не до конца обобщение в методе

        ...

        public static List<TClass> RandomizedFoodsLambda<TClass>(int amountOfFood = 40)
        {
            var rand = new Random(DateTime.Now.Millisecond);
            var randomizedFoods2 = new List<TClass>((IEnumerable<TClass>)Enumerable.
                Range(0, amountOfFood).Select(i => (FoodName)(rand).Next(0, 4)));   // не могу избавиться от FoodName
               // если меняю FoodName на TClass, to ошибка "Cannot convert type 'int' to 'TClass'"
            return randomizedFoods2;
        }

    var animalsCount = from animal in randomizedAnimals
        group animal by animal.Name into g
        select new { AnimalCategory = g.Key, CategoryCount = g.Count() };

    foreach (var groupedAnimal in animalsCount)
    {
        Console.WriteLine("{0} = {1}", groupedAnimal.AnimalCategory, groupedAnimal.CategoryCount);
    }