Iowa State University Veterinarian Records, RS 22/6/0/9, University Archives, Special Collections Department, Iowa State University, http://www.add.lib.iastate.edu/spcl/arch/rgrp/22-6-0-9.html
Human-animal bonds are forged through years of companionship and unconditional love offered in the midst of a hectic world where human relationships are often unstable. Pets offer not only companionship, but something to care for, something to touch and fondle, something to keep one busy, a focus of attention, a source of exercise, and safety. As social animals, people need a source of attachment, such as that provided by family or companion animals. For children, companion pets function as sibling substitutes. For childless adults, companion pets can be child substitutes. And for the introverted or lonely, companion pets may be considered by owners to be the only, or at least the best, confidants available. Therefore, when a pet dies, the degree of emotion experienced by these highly attached owners may equal the loss of a dose relative. The response to loss is grief; that state of mental and physical pain which is experienced when the loss of a significant object, person, or part of the self is realized.
Knodel, K. J. and Beran, George
"Breaking the Human-Animal Bond: Helping Clients Cope with Euthanasia,"
Iowa State University Veterinarian: Vol. 48
, Article 3.
Available at: https://lib.dr.iastate.edu/iowastate_veterinarian/vol48/iss2/3