I'm no expert, but fresh cow manure is high in nitrogen and also high in ammonia which can burn plant roots. Also, fresh cow manure is full of seeds, be it weed or grass seeds. In a garden, seeds from weeds or grasses are undesirable. Afterall, if you wanted to grow weeds or grasses, you wouln't be planting a garden in that area.
There have been discussions about disease being transferred from cows to humans via fresh cow manure. Granted that would be in a unhealthy herd and would also be mostly in root crops of leafy vegetables.
Now if you wanted to use fresh manure in the garden, I would suggest applying the manure in the fall and letting the garden "rest" until the spring. A good cultivation after spreading the manure and let it rot through the winter.
Overall, manure makes a great soil conditioner.