Depends on the WHOLE diet my friend! As the resident wether crazy lady, I want to encourage you to evaluate your water source, it really makes or breaks a diet. I have listed a few "safe diets" in this diagram that should help you achieve a good balance. As a general idea, timothy pellets usually have a pretty safe calcium to phosphorus ratio so that when added to the diet, harm is unlikely as long as you have a generally well-balanced diet. Are they needed? Not usually.