In the book "Rita Hayworth and the Shawshank Redemption" on page 26, Red says, "They give you life, and that is what they take- all of it that counts, anyway."
Dogs are loyal. Dogs, being domestic animals, are overly fond of humans that nurture and care for them that they develop strong feelings of loyalty toward their owners. They are being fed and given shelter by the humans and in turn, they would dedicate their selves to their human owners. Dogs are easily tamed animals as they live among humans and interact with them. Because of this interaction, they develop strong feelings of loyalty. Thus, dogs are loyal because of humans.
I believe this is true, because addressing the reader's name is sort of informal and not suitable in a cover letter.