Zoo shots aren't easy - mostly because the zoo hours usually provide very harsh lighting.
1. Nothing real wrong with this picture, but nothing to really capture my attention either. The giraffe's eye looks very dark. I am also not real fond of the trees that meet his muzzle. It is kind of like having an un-needed horizon line. Would have been a nicer shot if you could have angled to just have sky.
2. Rather boring, centered composition. Not sure what the cage was like, but it would have been nice if you could have gotten more on his level.
3. Is dark, but if lightened the coat will probably loose any detail it has.
With the last two, you really don't have to worry about getting all the limbs. You shouldn't just cut off the animals feet, but shots can be more interesting if not just a picture with the entire animal included in the middle of the shot. Nothing is wrong with any of them, they are just not real creative. The advantage of a zoo is that the animals are in a closed space, you basically have as long as you want to be there. Try different angles, avoid trying to take pictures of animals that are in bright, direct sunlight and take the time you need to think and compose the shots! The key to zoo shooting is patience (as in with most photography).