You are making a common mistake for random numbers.
See the MSDN Documentation on Random
Random numbers are actually pseudo random and the clock is used by default for its seed (you can provide your own though).
To solve, you can make a single random object and have your own seed value (int) rather than the default.
Random _randSeed = new Random(GetSavedSeedValue());
if (seconds % 5 == 0 && seconds != 0 && animal_appearance == false)
animal_appearance = true;
Last_animal += seconds;
anime_Index = _randSeed.Next(9);