Why do my cattles and sheeps grow so slow? I have fed them so much fresh hay?

Even fresh hay grass is only called roughage forage (coarse fodder). Roughage includes pasture, crop straw, vinasse, and so on. If cattle/sheep only eat roughage, it will cause nutrition imbanlance and slow growth. If you want to improve feeding effect, and make animals grow faster, make some concentrated feed pellets for them!